My design mapped in a previous revision of ISE with no problems. I have not changed the I/O configurations, but now the design fails in version 9.1i with IOSTANDARD errors:
"ERROR:Pack - The I/O component "SPI4_RDAT1_N" has an illegal IOSTANDARD
value. The IOB component is configured to use differential signaling and can
not use single-ended IOSTANDARD value LVCMOS25. Please correct the
IOSTANDARD property value or the I/O connectivity."
In version 9.1i, MAP no longer attempts to correct illegal IOSTANDARDs or unspecified IOSTANDARDs by assigning a default value. Consequently, errors can occur that did not occur in previous revisions. You can restore the automatic correction of IOSTANDARDS by setting the following applicable environment variable:
setenv XIL_MAP_FIXIOSTD 1
For general information on setting the ISE environment variable, see (Xilinx Answer 11630).