At the moment ikvm/runtime/JniInterface.cs contains the following workaround:

#if __MonoCS__ 
  // MONOBUG mcs requires this bogus fixed construct (and Microsoft doesn't allow it)
  fixed(void** p = &pJavaVM->firstVtableEntry) { pJavaVM->vtable = p; }
#else
  pJavaVM->vtable = &pJavaVM->firstVtableEntry;
#endif

Up until Mono 1.1.4 this workaround is required, but current Mono svn has a fixed mcs that doesn't require (nor allow) the workaround.

This means that current IKVM cvs isn't compilable with current Mono svn and that's dumb. The proper way to fix mcs would have been to temporarily (at least until after the next Mono release) allow the incorrect usage of fixed and issue a warning that such usage is illegal and will stop working in a future release.