Although you haven't provided many specific details about the crash, I would highly recommend using the Mono Migration Analyzer to find any problems.
The Mono Migration Analyzer (MoMA) is a tool designed by the Mono team to test whether your program makes any unsafe calls in its source code, or calls any unimplemented functions. The tool should list any problematic calls or lines of code which you could try replacing with a Mono-friendly equivalent.
You can download MoMA here. It's recently become unsupported, but works well for the recent releases of Mono.
Sorry I couldn't provide a concrete answer to your question, but this is impossible to do without more details about your setup. If using MoMA does not help you, the rest of the Game Development Community and I would be happy to help you if you provided more details.