Poweredge 800 compatible memory - ECC only?

Right now I am using non-ECC RAM in the PE800 with no problems.

BIOS has ECC memory as an unchanged spec.  Manual states ECC.

Crucial.com notes states can use all non-ECC or all ECC, but they will only recommend ECC modules - CT12872AA667.

Bought non -ECC figuring could use it in future desktop.

In it is Samsung M378T6553CZ3-CD5  1Rx8  pc2-4200 512mb x2

and     Samsung M378T6553EZS-CE6  1Rx8 pc2-5300 512mb x2.

REJECTED - no POST - Crucial CT12864AA667.M8FJ1  (8F means 8 chips)  1GB.

Rejected if Crucial - 1 stick or both, or combined with Samsung.  Fails Post.

All are unbuffered unregistered, and the Samsung in CPU-Z has Error correction = NONE.

 

Can the Poweredge 800 use non-ECC ram in general?   Did I just get lucky with the Samsung?

Could the higher density (1Rx8) 1GB vs (1Rx8) 512mb be the problem?

Has anyone successfully used the Crucial CT12864AA667 instead of CT12872AA667?