The following programming practices can be the cause of this problem:
software delay loops; word or longword access of an odd address (illegal
on the 68000).  Note that this can occur under 2.0 if you reference
IntuiMessage->IAddress as a structure pointer without first determining
that the IntuiMessage's Class is defined as having a structure pointer in
its IAddress; use of the assembler CLR instruction on a hardware register
which is triggered by any access.  The 68000 CLR instruction performs two
accesses (read and write) while 68020/30 CLR does a single write access.
Use MOVE instead; assumptions about the order in which asynchronous tasks
will finish; use of compiler flags which have generated inline 68881/68882
math coprocessor instructions or 68020/30 specific code.