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	2010-03-27 10:12:14.667366971 +0000
+++ system-config-printer-1.2.0/asyncipp.py	2010-03-27 10:13:04.081365616 +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
diff -up system-config-printer-1.2.0/asyncpk1.py.asyncipp-traceback system-config-printer-1.2.0/asyncpk1.py
--- system-config-printer-1.2.0/asyncpk1.py.asyncipp-traceback	2010-03-27 10:12:14.702364469 +0000
+++ system-config-printer-1.2.0/asyncpk1.py	2010-03-27 10:13:06.407243790 +0000
@@ -64,6 +64,7 @@ class _PK1AsyncMethodCall:
         self._fallback_fn = fallback_fn
         self._fallback_args = args
         self._fallback_kwds = kwds
+        self._destroyed = False
         debugprint ("+_PK1AsyncMethodCall: %s" % self)
 
     def __del__ (self):
@@ -85,6 +86,7 @@ class _PK1AsyncMethodCall:
 
     def _destroy (self):
         debugprint ("DESTROY: %s" % self)
+        self._destroyed = True
         del self._bus
         del self._conn
         del self._pk_method_name
@@ -97,6 +99,9 @@ class _PK1AsyncMethodCall:
         del self._fallback_kwds
 
     def _pk_reply_handler (self, error, *args):
+        if self._destroyed:
+            return
+
         if str (error) == '':
             self._client_reply_handler (self._conn, self._unpack_fn (*args))
             self._destroy ()
@@ -106,6 +111,9 @@ class _PK1AsyncMethodCall:
         self.call_fallback_fn ()
 
     def _pk_error_handler (self, exc):
+        if self._destroyed:
+            return
+
         if exc.get_dbus_name () == CUPS_PK_NEED_AUTH:
             exc = cups.IPPError (cups.IPP_NOT_AUTHORIZED, 'pkcancel')
             self._client_error_handler (self._conn, exc)
@@ -123,10 +131,16 @@ class _PK1AsyncMethodCall:
         self._fallback_fn (*self._fallback_args, **self._fallback_kwds)
 
     def _ipp_reply_handler (self, conn, *args):
+        if self._destroyed:
+            return
+
         self._client_reply_handler (self._conn, *args)
         self._destroy ()
 
     def _ipp_error_handler (self, conn, *args):
+        if self._destroyed:
+            return
+
         self._client_error_handler (self._conn, *args)
         self._destroy ()