diff -up system-config-printer-1.2.0/asyncipp.py.asyncipp-traceback system-config-printer-1.2.0/asyncipp.py
--- system-config-printer-1.2.0/asyncipp.py.asyncipp-traceback	2010-03-26 12:50:39.829627667 +0000
+++ system-config-printer-1.2.0/asyncipp.py	2010-03-26 12:50:51.888627367 +0000
@@ -59,6 +59,7 @@ class _IPPConnectionThread(threading.Thr
         self._auth_handler = auth_handler
         self._auth_queue = Queue.Queue (1)
         self.user = None
+        self._destroyed = False
         debugprint ("+%s" % self)
 
     def __del__ (self):
@@ -157,6 +158,7 @@ class _IPPConnectionThread(threading.Thr
             self._queue.task_done ()
 
         debugprint ("Thread exiting")
+        self._destroyed = True
         del self._conn # already destroyed
         del self._reply_handler
         del self._error_handler
@@ -188,21 +190,23 @@ class _IPPConnectionThread(threading.Thr
         return password
 
     def _reply (self, result):
-        def send_reply (result):
-            self._reply_handler (self._conn, result)
+        def send_reply (handler, result):
+            if not self._destroyed:
+                handler (self._conn, result)
             return False
 
-        if self._reply_handler:
-            gobject.idle_add (send_reply, result)
+        if not self._destroyed and self._reply_handler:
+            gobject.idle_add (send_reply, self._reply_handler, result)
 
     def _error (self, exc):
-        def send_error (exc):
-            self._error_handler (self._conn, exc)
+        def send_error (handler, exc):
+            if not self._destroyed:
+                handler (self._conn, exc)
             return False
 
-        if self._error_handler:
+        if not self._destroyed and self._error_handler:
             debugprint ("Add %s to idle" % self._error_handler)
-            gobject.idle_add (send_error, exc)
+            gobject.idle_add (send_error, self._error_handler, exc)
 
 ###
 ### This is the user-visible class.  Although it does not inherit from