Forms 10g crashes calling a DLL

We are upgrading a Forms application from 6i to 10g.  One form has ORA_FFI commands to call a DLL to encrypt or decrypt a password.  We are using WEBUTIL.C_API in 10g in place of ORA_FFI to interface with the DLL.  However, the form crashes at runtime,calling the DLL, and gives us a log file with a lot of Java messages which do not give us meaningful explanations.  Can someone give us some tips on where to look and how to properly interface with DLLs.  Thanks in advance.
Hetal