Which client do you use with what release of CMOD?
Answer: the newest one possible.
http://www-01.ibm.com/support/docview.wss?uid=swg21392275
In that I must agree strongly :-) I had a few weeks ago a customer with an AFP problem, and it was working fine with Client 8.4.X, but the 8.5.X series didn't play nice, and they had lots of problems.
They tried 9.0.0.0 without success.
Then they call me, and I tried the new 9.0.0.1 client... and guess what, it worked! :-D
Well sometimes this is a lottery! :-D