Memory upgrade PowerEdge 1800, POST okay, OS won't boot

Upgraded a PowerEdge 1800 Server from 2GB to 4GB of ram. Installed two additional DIMMs of the following type:

• 240Pin DDR2
• PC3200 400MHz
• ECC Registered
• Dual Rank (must install in sets of 2) 

Server will complete POST but Windows Server 2003 OS will not start completely. Gets about halfway through loading and reboots. Removed two of the DIMMs and the server functions normally. Swapped all 4 DIMMs with matching memory from another dell server and ran into the exact same problem.

I ran the complete test from the dell diagnostics utility on CD and the hardware/new memory checked out.

• Dell Diagnostics Utility
• 32 Bit Diagnostics
• Date: 10/23/2008
• Version: 5109A1, 5109.2

Suggestions?

Thanks,

Scott