simulate EP2C35 development board but encouter fatal errors.

ModelSim works somewhat different than a HDL compiler, it's processing part of the code at runtime. Some errors, particularly range errors with indexes or overflow of variables is causing a runtime error. It's not certainly a real eror, some overflows are causing normal behaviour in RTL, only needing special handling with ModelSim. In your case, it looks like a real coding error, but this can't be seen without looking into the code, at the error location said in the message.