An XPLA3 Coolrunner design that FIT in ISE 8.2 no longer FITs in ISE 9.1. It issues the following error message:
ERROR:Cpld:1061 - Design contains xx unique asynchronous resets and presets,
exceeds device limit 1xx4.
ERROR:Cpld:1064 - Design rules checking error. Fitting process stopped.
This is a known issue for the XPLA3 Coolrunner family that is currently under investigation. To work around this, use ISE 8.2i.
This issue is scheduled to be fixed in 9.2i.