Index: twisted/spread/pb.py
===================================================================
--- twisted/spread/pb.py        (revision 12811)
+++ twisted/spread/pb.py        (working copy)
@@ -886,7 +886,15 @@
             netResult = object.remoteMessageReceived(self, message, netArgs, netKw)
         except Error, e:
             if answerRequired:
-                self._sendError(CopyableFailure(e), requestID)
+                # If the error is Copyable, send it back and let the code
+                # on the other end deal with unjellying.
+                # If it isn't Copyable, wrap it in a CopyableFailure, which
+                # ensures it can be unjellied on the other end.  We have to
+                # do this because all errors must be sent back.
+                if isinstance(e, Copyable):
+                    self._sendError(e, requestID)
+                else:
+                    self._sendError(CopyableFailure(e), requestID)
         except:
             if answerRequired:
                 log.msg("Peer will receive following PB traceback:", isError=True)