diff --git a/secop/client/__init__.py b/secop/client/__init__.py
index a3d3b9b..68070d4 100644
--- a/secop/client/__init__.py
+++ b/secop/client/__init__.py
@@ -107,21 +107,21 @@ class ProxyClient:
         # caches (module, parameter) = value, timestamp, readerror (internal names!)
         self.cache = {}
 
-    def register(self, key, obj=None, **kwds):
+    def register_callback(self, key, *args, **kwds):
         """register callback functions
 
-        - kwds each key must be a valid callback name defined in self.CALLBACK_NAMES
-        - kwds values are the callback functions
-        - if obj is not None, use its methods named from the callback name, if not given in kwds
         - key might be either:
             1) None: general callback (all callbacks)
             2) <module name>: callbacks related to a module (not called for 'unhandledMessage')
             3) (<module name>, <parameter name>): callback for specified parameter (only called for 'updateEvent')
+        - all the following arguments are callback functions. The callback name may be
+          given by the keyword, or, for non-keyworded arguments it is taken from the
+          __name__ attribute of the function
         """
+        for cbfunc in args:
+            kwds[cbfunc.__name__] = cbfunc
         for cbname in self.CALLBACK_NAMES:
             cbfunc = kwds.pop(cbname, None)
-            if obj and cbfunc is None:
-                cbfunc = getattr(obj, cbname, None)
             if not cbfunc:
                 continue
             cbdict = self.callbacks[cbname]
diff --git a/secop/gui/mainwindow.py b/secop/gui/mainwindow.py
index 6c0cd3d..afda457 100644
--- a/secop/gui/mainwindow.py
+++ b/secop/gui/mainwindow.py
@@ -55,7 +55,7 @@ class QSECNode(QObject):
         self.modules = conn.modules
         self.properties = self.conn.properties
         self.protocolVersion = conn.secop_version
-        conn.register(None, self)  # generic callback
+        conn.register_callback(None, self.updateEvent, self.nodeStateChange, self.unhandledMessage)
 
     # provide methods from old baseclient for making other gui code work
 
@@ -81,7 +81,10 @@ class QSECNode(QObject):
         return self.conn.getParameter(module, parameter, True)
 
     def execCommand(self, module, command, arg):
-        return self.conn.execCommand(module, command, arg)
+        try:
+            return self.conn.execCommand(module, command, arg)
+        except Exception as e:
+            return 'ERROR: %r' % e, {}
 
     def queryCache(self, module):
         return {k: Value(*self.conn.cache[(module, k)])
diff --git a/secop/protocol/router.py b/secop/protocol/router.py
index 019fc20..3d3c93a 100644
--- a/secop/protocol/router.py
+++ b/secop/protocol/router.py
@@ -70,10 +70,9 @@ class SecopClient(secop.client.SecopClient):
                     self.updateEvent(*key, *self.cache[key])
 
     def descriptiveDataChange(self, module, data):
-        print('CHANGE', self.nodename)
+        if module is None:
+            self.log.error('descriptive data for node %r has changed', self.nodename)
         self.dispatcher.restart()
-        #if module is None:
-        #    self.log.error('descriptive data for node %r has changed', self.nodename)
 
 
 class Router(secop.protocol.dispatcher.Dispatcher):
@@ -99,7 +98,7 @@ class Router(secop.protocol.dispatcher.Dispatcher):
             self.nodes = [SecopClient(uri, logger.getChild('routed%d' % i), self) for i, uri in enumerate(uris)]
         # register callbacks
         for node in self.nodes:
-            node.register(None, node)
+            node.register_callback(None, node.updateEvent, node.descriptiveDataChange, node.nodeStateChange)
         self.node_by_module = {}
         multievent = MultiEvent()
         for node in self.nodes:
@@ -113,7 +112,7 @@ class Router(secop.protocol.dispatcher.Dispatcher):
                 nodes.append(node)
             else:
 
-                def check_new_node(online, state, self=self, node=node):
+                def nodeStateChange(online, state, self=self, node=node):
                     if online:
                         for module in node.modules:
                             self.node_by_module[module] = node
@@ -122,7 +121,7 @@ class Router(secop.protocol.dispatcher.Dispatcher):
                         return secop.client.UNREGISTER
                     return None
 
-                node.register(None, nodeStateChange=check_new_node)
+                node.register_callback(None, nodeStateChange)
                 logger.warning('can not connect to node %r', node.nodename)
 
     def handle_describe(self, conn, specifier, data):
diff --git a/secop/proxy.py b/secop/proxy.py
index 1686a72..1791267 100644
--- a/secop/proxy.py
+++ b/secop/proxy.py
@@ -61,7 +61,8 @@ class ProxyModule(Module):
         if not self.module:
             self.properties['module'] = self.name
         self._secnode = self._iodev.secnode
-        self._secnode.register(self.module, self)
+        self._secnode.register_callback(self.module, self.updateEvent,
+                                        self.descriptiveDataChange, self.nodeStateChange)
         super().initModule()
 
     def descriptiveDataChange(self, module, moddesc):
@@ -147,7 +148,6 @@ class SecNode(Module):
 
     def earlyInit(self):
         self.secnode = SecopClient(self.uri, self.log)
-        self.secnode.register(None, self)  # for nodeStateChange
 
     def startModule(self, started_callback):
         self.secnode.spawn_connect(started_callback)