recognizing multiple fpga's

Hi All, We have a prototype board with 4 fpga's. One is an XC3S1500 and the others are XC3S200. There are a lot of jumpers so each one can be the only device on the chain. The bigger device is detected. But when the jumpers are set to individually select the small ones, they arent recognized and is listed as 'unknown device'. If anyone has seen something like this please do tell me what is wrong. Any help is highly appreciated. Thanks Subhasri.K