Precision 650 maximum memory and type

I own a Precision 650 that originally had 1GB RAM installed: four (4) 256MB DIMMs, DDR SDRAM, PC2100, ECC, unbuffered. I needed to upgrade a drive, so I decided I'd upgrade the memory while I had the machine open. Using Dell's memory selector along with my service tag, the following memory was recommended:

Manufacturer Part# SNPG2671C/1G, Dell Part# A0742831 (ECC) or

Manufacturer Part# SNPJ0203C/1G, Dell Part# A0740400 (non-ECC).

Both of these are 1GB DIMMs.

I decided to purchase four non-ECC modules and they are currently installed. I subsequently got Stop errors (a.k.a. "blue screen off death") about twice a day. Being suspicious of the memory, I ran Memtest 86+ for 24 hours straight with absolutely no errors. Doing more research on the specific stop codes, I learned that the problem could be related to SCSI communication errors. Since I was fiddling with the drives when I upgraded the memory, I switched the SCSI connector, re-seated all of the DIMMs, and did a general cleaning. I thought I had eliminated the Stop errors for good, but I just got another one the other day. It might still be the SCSI thing.

At this point, I got to thinking that I need to go back to ECC even though non-ECC should have been just fine (I'm not using the computer for a critical server operation). Is it possible that ECC memory would be compensating for SCSI communication errors that might lead to a memory page fault? (i.e., swapfile issue)

Looking into this, I found the following information stated for the allowable memory configuration on the original sales sheet for this computer: "256MB non-ECC DDR266 SDRAM standard; 4 DIMM slots; 2GB maximum: 128MB DIMM (ECC or non- ECC), 256MB DIMM (ECC or non- ECC), 512MB DIMM (ECC or non- ECC), 1GB DIMM (non-ECC only)." Note that for 1GB DIMMs, it is stated that only non-ECC memory can be used. This contradicts the memory suggested by Dell's memory selector. The statement also indicates 2GB as the maximum when, on the previous page of the sales sheet, 4GB is stated as the maximum. 4GB is also stated in the User’s Guide.

Here are the Sales Sheet and User's Guide (memory).

Can anyone explain the discrepancies? Are 1GB ECC modules okay? Is 4GB okay? Should I go down to 2GB ECC as 4 x 512MB modules? I know 4GB is overkill for Windows XP, but I got the four 1GB modules cheap.

I'm looking at you, Dell.