The XC3S1200E-4 and XC3S1600E-4 devices might fail a Verify in iMPACT. These devices will also not support the CFG_OUT command, and a readback will not be possible with these devices.
The issue will affect all package combinations for the -4 speedgrade of these two families of devices.
The problem is inherent to the devices and some of the devices will fail a Verify in iMPACT. The devices might read out the wrong values for the configuration memory locations that it is reading. The configuration memory might not be wrong, but the values read out of the device in this manner could be reported wrong. In this scenario, a Verify will fail but the device might be operational. If this is the case, check the functionality on the board to ensure the device is working properly.