This is an intermittent problem that some computers have with the cables. This problem occurs only because of an issue with the Parallel Port. The USB Platform Cable is not affected by this problem; therefore, it can be used at 6 MHz.
An updated version of the PCIV cable firmware is being field tested. This version improves cable operation, and should fix communication problems reported by a small population of customers. If you are interested in trying this fix, contact Xilinx Technical Support:
http://www.xilinx.com/support/services/contact_info.htmMake sure there is no other software using the parallel port to access hardware. This could be in the form of a printer, dongle, or other software looking for hardware on the parallel port.
Change the cable speed in iMPACT operating on the cable by selecting Output -> Cable Setup. If the problem is with the Parallel-IV cable, try connecting as a Parallel-III cable in the Cable Setup menu.
Try using the 6.3.03 release of iMPACT, if this software is available.
If you are still experiencing problems, contact Xilinx Technical Support:
http://www.xilinx.com/support/services/contact_info.htm.