When running PAR in ISE 10.1, I see the following error:
"ERROR:PAR:424 - Invalid Installation. License could not be acquired"
PAR checks whether run in full mode or eval mode by reading your entitlement information from the .ui.dat license file found in the folder above $Xilinx. If this file does not exist in this location or is corrupt, this message would be seen. Please either move the file to the correct location or reinstall ISE 10.1.