Program commit suicide when exiting callBack

[shaCo]

im calling an extern method from a dll written in c (i think) .
the method is supposed to get a callBack function , so im sending it a delegete.
the method is working fine, and my callback is called ok, but when it reaches the ending block of the callback i get an error message like this :
0xC0000005: Access violation reading location 0x00000000.

the callBack has a return type of uint32 which is always 0 .
(i dont know if its releated because the error comes after the 'return' command)

which hammer should i buy to get it working?