Xilinx XC2S50: Unable to configure through slave serial mode

Hi

I am trying to build a prototype Spartan-II board.

1. I am using a XC2S50 TQ144 part with all the mode pins tied to VCCINT
2. I am using Xilinx webpack 4.2
3. The parallel cable is from insight electronics (Model IJC-2)
4. I am using a general purpose PCB and a QFP144 adapter from adapters.com to connect the FPGA to the PCB.

Now when I compile a simple test module and try to download the bit file through Xilinx iMPACT tool, it gives an error saying "Configuration failed: done pin did not go high".

What could be the cause and how can I debug it.

Thanks Sumit