Per PCN2003-04 (http://www.xilinx.com/support/documentation/customer_notices/pcn2003-04.pdf), Xilinx added a new vendor for manufacturing 18V00 devices. Specifically, we added STMicro and retained UMC. The PCN has this statement about compatibility: The STMicroelectronics offerings will be form, fit, and functionally compatible with the current product. The JTAG IDCODES will differ.
From iMPACT 12.1, we are only supporting the STMicro devices and the IDCODE from the UMC devices is not supported. To program older devices, revert to 11.x.
Or,hand edit the BSDL file and change bit 16 to a '0' or to an 'X' (don't care) if you have mixed UMC STMicro parts. The '1'-- "required by standard" bit being the LSB bit 0.
--snipit from BSD file--
attribute IDCODE_REGISTER of XC18V02: entity is
XXXX" & -- version
"0101000000110101" & -- part number
"00001001001" & -- manufacturer's id
"1"; -- required by standard.