So finally went to log into my routers today and the one I had put the 2 x 256mb boards that came with the routers in worked fine.
The two that i put the 512mb boards in of non-ecc ddr1 memory that i got from ebay (link below) did not work and instead returned the error message... "ERROR: Unsupported DIMM memories in DIMM SLOT:00000000"
Corsair 4 x 512MB = 2GB PC2700 (333), 184PIN, DDR1 Desktop RAM Memory NEW SEALED | eBay
So I guess I need to search for and buy Cisco 2811 memory only...