I have both ISE version 6.3.03i and version 7.1i installed in separate directories on my computer. My Platform Cable USB worked fine with iMPACT in 6.3.03i, and it continued to work fine when I migrated to 7.1i. However, I switched back to 6.3.03i (by setting the XILINX and PATH environment variables) and now iMPACT either fails to identify the devices in a JTAG chain, or it returns the following error message when I attempt a configuration operation (e.g., Program, Verify, Erase, etc.):
"ERROR:iMPACT:583, or devices are detected as UNKNOWN."
The Platform Cable USB firmware released with iMPACT version 7.1 and later is not backwards-compatible with iMPACT version 6.3.03i; however, a patch is available that resolves this problem:
Once you have downloaded the ZIP file, extract the files and then follow the steps in the "README_FIRST.pdf" file.
When the patch is installed, you should be able to switch back and forth between 7.1i and 6.3.03i (by setting the XILINX and PATH environment variables) and the Platform Cable USB should function seamlessly.