[Twisted-Python] Traceback from pb-Server

[Stephan Popp]

Hi,
Please excuse my bad english, I hope you will understand what I mean, 
otherwise feel free to ask.
I'm trying to get error messages from my server. I'm using twisted 2.0.0 with 
python 2.4.
The server looks like this:

from twisted.spread import pb
from twisted.internet import reactor, threads

class ServerObject(pb.Root):

#...some other methods, which aren't involved...

def remote_fitness(self, task, taskDescription, serverID):
	return threads.deferToThread(self.calc, task, serverID, taskDescription)

def calc(self, task, serverID, taskDescription):
	exec('from %s import %s as func' % 
(taskDescription.fileName,taskDescription.functionName))
#problem: file specified in fileName needn't to be in working directory of 
server
	func(task) #calulates something
	return task

if __name__ == '__main__':
	factory = pb.PBServerFactory(ServerObject())
	reactor.listenTCP(8800, factory)
	reactor.run() 

The client calls, after connection is made.
def1 = root.call_remote("fitness", task, taskDescription, serverID)
def1.addCallback(self.serverCB)
def1.addErrback(self.serverErrorCB)

def serverErrorCB(self, reason):
	print reason

If the pythonscript named taskDescription.fileName isn't there 
self.serverErrorCB is called - thats ok. But it prints:
reason [Failure instance: Traceback from remote host -- Traceback unavailable]

But I need to know why the call failed. Can anyone please help me to get the 
traceback or the exception message that the server prints 
(exceptions.ImportError: No module named fitfunc2).