Source: by Mike Kazantsev
Upstream: http://code.google.com/p/pyicqt/issues/detail?id=179
Reason:

 Unhandled error in Deferred:
 Traceback (most recent call last):
 File "/usr/lib64/python2.7/site-packages/pyicqt/src/tlib/oscar.py", line 663, in dataReceived
 state=func(flap)
 File "/usr/lib64/python2.7/site-packages/pyicqt/src/tlib/oscar.py", line 805, in oscar_Data
 d.errback(snac)
 File "/usr/lib64/python2.7/site-packages/twisted/internet/defer.py", line 388, in errback
 self._startRunCallbacks(fail)
 File "/usr/lib64/python2.7/site-packages/twisted/internet/defer.py", line 455, in _startRunCallbacks
 self._runCallbacks()
 --- <exception caught here> ---
 File "/usr/lib64/python2.7/site-packages/twisted/internet/defer.py", line 542, in _runCallbacks
 current.result = callback(current.result, *args, **kw)
 File "/usr/lib64/python2.7/site-packages/pyicqt/src/tlib/oscar.py", line 2097, in _cbRequestSSI
 if snac[1] == 0x0f: # same SSI as we have
 exceptions.TypeError: 'NoneType' object is not subscriptable

  Looking at the code, it looks like proper snac (not None) is passed to
 errback chain but is get lost somewhere on the way to _cbRequestSSI.

  _ebDeferredError seem to be the first errback for these deferreds and it
 doesn't seem to return anything and indicates a critical errors, so it looks
 like either adding callbacks after that errback (so they'll be processed
 after it with None argument) is wrong or errback itself should re-raise error
 (or return a Failure object) to pass it to next errback, not the callback
 chain.

 Patch returns the same Failure, so further errbacks
 (_ebDeferredRequestSSIError) should be called in case of errors instead of
 callbacks (_cbRequestSSI).

diff --git a/src/tlib/oscar.py b/src/tlib/oscar.py
index befba43..5e5bed8 100644
--- a/src/tlib/oscar.py
+++ b/src/tlib/oscar.py
@@ -756,6 +756,7 @@ class SNACBased(OscarConnection):
 		log.msg('On sending of message, family 0x%02x, subtype 0x%02x' % (fam, sub))
 	if showdata:
 		log.msg('data not sent: %s' % repr(data))
+	return error
 
     def sendSNACnr(self,fam,sub,data,flags=[0,0]):
         """