Does anyone know of problems when increasing to 2GB RAM for ASUS P5S800-VM

I have an ASUS P5S800-VM mb with a Celeron D that runs RedHat 7.0 in text mode and the original 512MB was fine for a while. Its primary use is as a server for telnet connections to a COBOL pharmacy operations and POS app. As new demands have been placed on the ASUS, especially a Java electronic signature capture application, it has really slowed down. I bought a 2GB Corsair Value Select kit of DDR 400MHz, approved for the ASUS on the Corsair Memory Finder. The ASUS will not complete a RAM check with either or both of the new Corsair 1GB DIMM’s. I got an RMA from Corsair, but I’m just wondering if maybe I’m missing something.