usage of PAL_TRY

Hi,
 in the process of making changes to the garbage collector, i added a few
PAL_TRY blocks in gcsmp.cpp. of the following form
 PAL_TRY {
  ..
  if(error) PAL_LEAVE_EX(labelxx);
 }
 PAL_EXCEPT_FILTER_EX(labelxx, HandleGCException, NULL) {
 ..
 }
 PAL_ENDTRY

but when i debug a simple application, i get the following Assert at the
first PAL_ENDTRY that i added..
{0804D000} ASSERT [EXCEPT ] at ../exception.c.442: Exception registration
pointers don't match!

and if i comment all these it throws up the same assert at another point,
in appdomain.cpp (SystemDomain::CreatePreallocatedExceptions) at the
COMPLUS_CATCH statement.
can you please help.

Thanks and regards,
archana