Precision T3420 ECC RAM options

I've been trying to find what I can about some ECC ram options since im turning this bad boy into a storage server of sorts.

Problem:I installed two sticks of SAMSUNG 8GB 288-Pin DDR4 SDRAM ECC Registered DDR4 2133 1Rx4  (m393a1g40db0-cpb) and it wont boot at all (good thing it was free)

Problem cont.: Dell ram is morbidly expensive

Im looking to see if anyone has had success using any other ECC ram besides the dell ram.

Also, Dell states that there are both 2400 and 2133MHz options...does this MB support 2400MHz natively? My CPU doesnt (1245v5) :Crying:

At the end of the day...can i just get any unbuffered 2Rx8 ECC ram? Even though 1Rx8 is also listed as compatible. I am curious if the samsung ram i have didnt work because it is registered? or because of the 1Rx4 ranking?

Thanks in advance