diff --git a/src/cutecoin/core/person.py b/src/cutecoin/core/person.py
index 67c0419b2b46c7b602fd2b5e4fe839c1cbd886a2..7a1a14c66515434f794049062d86879cc0d72968 100644
--- a/src/cutecoin/core/person.py
+++ b/src/cutecoin/core/person.py
@@ -79,19 +79,23 @@ class Person(object):
         raise PersonNotFoundError(self.pubkey, community.name())
 
     def membership(self, community):
-        search = community.request(bma.blockchain.Membership,
-                                           {'search': self.pubkey})
-        block_number = 0
-        for ms in search['memberships']:
-            if ms['blockNumber'] >= block_number:
-                if 'type' in ms:
-                    if ms['type'] is 'IN':
+        try:
+            search = community.request(bma.blockchain.Membership,
+                                               {'search': self.pubkey})
+            block_number = 0
+            for ms in search['memberships']:
+                if ms['blockNumber'] >= block_number:
+                    if 'type' in ms:
+                        if ms['type'] is 'IN':
+                            membership_data = ms
+                    else:
                         membership_data = ms
-                else:
-                    membership_data = ms
 
-        if membership_data is None:
-            raise MembershipNotFoundError(self.pubkey(), community.name())
+            if membership_data is None:
+                raise MembershipNotFoundError(self.pubkey, community.name())
+        except ValueError as e:
+            if '400' in str(e):
+                raise MembershipNotFoundError(self.pubkey, community.name())
 
         membership = Membership(PROTOCOL_VERSION, community.currency, self.pubkey,
                                 membership_data['blockNumber'],
diff --git a/src/cutecoin/gui/certification.py b/src/cutecoin/gui/certification.py
index 7ff30f863818a942f0826b150a840ad07165f399..1492c6cd4fb2ac1b8b750fbea775852753aaf113 100644
--- a/src/cutecoin/gui/certification.py
+++ b/src/cutecoin/gui/certification.py
@@ -3,7 +3,7 @@ Created on 24 dec. 2014
 
 @author: inso
 '''
-from PyQt5.QtWidgets import QDialog, QMessageBox
+from PyQt5.QtWidgets import QDialog, QMessageBox, QDialogButtonBox
 from ..tools.exceptions import NoPeerAvailable
 from ..gen_resources.certification_uic import Ui_CertificationDialog
 
@@ -20,11 +20,11 @@ class CertificationDialog(QDialog, Ui_CertificationDialog):
         '''
         super().__init__()
         self.setupUi(self)
-        self.certifier = certifier
+        self.account = certifier
         self.password_asker = password_asker
-        self.community = self.certifier.communities[0]
+        self.community = self.account.communities[0]
 
-        for community in self.certifier.communities:
+        for community in self.account.communities:
             self.combo_community.addItem(community.currency)
 
         for contact in certifier.contacts:
@@ -33,7 +33,7 @@ class CertificationDialog(QDialog, Ui_CertificationDialog):
     def accept(self):
         if self.radio_contact.isChecked():
             index = self.combo_contact.currentIndex()
-            pubkey = self.certifier.contacts[index].pubkey
+            pubkey = self.account.contacts[index].pubkey
         else:
             pubkey = self.edit_pubkey.text()
 
@@ -42,7 +42,7 @@ class CertificationDialog(QDialog, Ui_CertificationDialog):
             return
 
         try:
-            self.certifier.certify(password, self.community, pubkey)
+            self.account.certify(password, self.community, pubkey)
             QMessageBox.information(self, "Certification",
                                  "Success certifying {0} from {1}".format(pubkey,
                                                                           self.community.currency))
@@ -65,7 +65,11 @@ class CertificationDialog(QDialog, Ui_CertificationDialog):
         super().accept()
 
     def change_current_community(self, index):
-        self.community = self.certifier.communities[index]
+        self.community = self.account.communities[index]
+        if self.account.pubkey in self.community.members_pubkeys():
+            self.button_box.button(QDialogButtonBox.Ok).setEnabled(True)
+        else:
+            self.button_box.button(QDialogButtonBox.Ok).setEnabled(False)
 
     def recipient_mode_changed(self, pubkey_toggled):
         self.edit_pubkey.setEnabled(pubkey_toggled)
diff --git a/src/cutecoin/gui/currency_tab.py b/src/cutecoin/gui/currency_tab.py
index ef3e74bc950eab7b29a2163b60fe36cf00ecc7ba..8b9ffc5fef548056802b77bb21125b9ee9500f83 100644
--- a/src/cutecoin/gui/currency_tab.py
+++ b/src/cutecoin/gui/currency_tab.py
@@ -21,7 +21,7 @@ from ..models.txhistory import HistoryTableModel, TxFilterProxyModel
 from .informations_tab import InformationsTabWidget
 from ..models.wallets import WalletsListModel
 from ..models.wallet import WalletListModel
-from ..tools.exceptions import NoPeerAvailable
+from ..tools.exceptions import NoPeerAvailable, MembershipNotFoundError
 from ..core.wallet import Wallet
 from ..core.person import Person
 from ..core.transfer import Transfer
@@ -93,23 +93,26 @@ class CurrencyTabWidget(QWidget, Ui_CurrencyTabWidget):
         self.watcher_thread.start()
 
         person = Person.lookup(self.app.current_account.pubkey, self.community)
-        join_block = person.membership(self.community).block_number
-        join_date = self.community.get_block(join_block).mediantime
-        parameters = self.community.get_parameters()
-        expiration_date = join_date + parameters['sigValidity']
-        current_time = time.time()
-        sig_validity = self.community.get_parameters()['sigValidity']
-        warning_expiration_time = int(sig_validity / 3)
-        will_expire_soon = (current_time > expiration_date - warning_expiration_time)
-
-        if will_expire_soon:
-            days = QDateTime().currentDateTime().daysTo(QDateTime.fromTime_t(expiration_date))
-            QMessageBox.warning(
-                self,
-                "Membership expiration",
-                "Warning : Membership expiration in {0} days".format(days),
-                QMessageBox.Ok
-            )
+        try:
+            join_block = person.membership(self.community).block_number
+            join_date = self.community.get_block(join_block).mediantime
+            parameters = self.community.get_parameters()
+            expiration_date = join_date + parameters['sigValidity']
+            current_time = time.time()
+            sig_validity = self.community.get_parameters()['sigValidity']
+            warning_expiration_time = int(sig_validity / 3)
+            will_expire_soon = (current_time > expiration_date - warning_expiration_time)
+
+            if will_expire_soon:
+                days = QDateTime().currentDateTime().daysTo(QDateTime.fromTime_t(expiration_date))
+                QMessageBox.warning(
+                    self,
+                    "Membership expiration",
+                    "Warning : Membership expiration in {0} days".format(days),
+                    QMessageBox.Ok
+                )
+        except MembershipNotFoundError as e:
+            pass
 
     def refresh(self):
         if self.app.current_account is None:
diff --git a/src/cutecoin/models/txhistory.py b/src/cutecoin/models/txhistory.py
index e91eea080cf5c22d1639a89271a04a17a6dda27e..4e6cbb5f87c9aafd65078652d8059f7e33309460 100644
--- a/src/cutecoin/models/txhistory.py
+++ b/src/cutecoin/models/txhistory.py
@@ -79,14 +79,13 @@ class TxFilterProxyModel(QSortFilterProxyModel):
                 if source_data is not "":
                     amount_ref = self.account.units_to_diff_ref(source_data,
                                                                 self.community)
-                    ref_name = self.account.diff_ref_name(self.community.short_currency)
 
                     if type(amount_ref) is int:
-                        formatter = "{0} {1}"
+                        formatter = "{0}"
                     else:
-                        formatter = "{0:.2f} {1}"
+                        formatter = "{0:.2f}"
 
-                    return formatter.format(amount_ref, ref_name)
+                    return formatter.format(amount_ref)
 
         if role == Qt.FontRole:
             font = QFont()