diff --git a/tipbot.py b/tipbot.py
index 60bb3f8..fdd8f55 100644
--- a/tipbot.py
+++ b/tipbot.py
@@ -163,7 +163,11 @@ def LinkAccount(link,cmd):
   if linked_identity == None:
     link.send('usage: !link_account [<network>:]<username>')
     return
-  linked_identity=IdentityFromString(link,linked_identity)
+  try:
+    linked_identity=IdentityFromString(link,linked_identity)
+  except Exception,e:
+    link.send('%s is invalid' % linked_identity)
+    return
   ok,reason=LinkCore(link,linked_identity)
   if not ok:
     link.send('An error occured')
diff --git a/tipbot/utils.py b/tipbot/utils.py
index cd7adee..5a70a4a 100644
--- a/tipbot/utils.py
+++ b/tipbot/utils.py
@@ -381,6 +381,9 @@ def IdentityFromString(link,s):
     parts=s.split(':')
     network_name=parts[0]
     network=GetNetworkByName(network_name)
+    if not network:
+      log_error('unknown network: %s' % network_name)
+      raise RuntimeError('Unknown network: %s' % network_name)
     nick=parts[1]
   return network.name+':'+network.canonicalize(nick)