If you are running into the following error (Adept, or other programmer), here is how to fix it in Xilinx. I came across this issue when using my Basys 2 and trying to load a bit file with Digilent's Adept programmer. It is only a compatibility issue with the bit file and FPGA board. Startup clock for this file is'CCLK' instead of 'JTAG CLK'. Problems will likely occur. Associate config file with device anyway? In the Processes pane, select Generate Programming File Then go to Process -> Process Properties -> Startup Options -> FPGA Start-Up Clock and change it to JTAG CLK. Click, OK. Then re-generate the programming file and program your board.