Problem with Return Address

[ArC]

I got an application which calls a MFC function.
That MFC function calls another MFC function.
Now my problem:
As you know, when a call is executed, the return
address is pushed on the stack.
But not in this case:
When that MFC function calls the other MFC function,
0 is pushed on the stack as return address instead of
the real return address.
The result of this is that when that call
returns, the app crashes.

So how can this happen?

Notice:
That application is protected.
In the protected version of the app
that problem does not seem to occur.
However, I've unpacked that app by hand
and now I got this problem.

Thx