Here is what you said, which is what lead me to believe you were mixing DIMM's: >>Removing the RDIMM's from slot 5 and 6 resulted in the system working normally. All the RDIMM's are healthy, the ones pulled from 5 & 6, work in 3&4, not to mention this RAM was pulled from a functioning server to begin with.<< We can only ascertain so much from the information you provide to us and I do apologize for the assumption.  Now that we have established you do have UDIMM's and not RDIMM's, we can tell you that guide book is correct on UDIMM's.  It will only support  8gb of RAM using 2gb  UDIMM's, in 4 slots or 16gb using 4gb UDIMM's.   RDIMM's are supported in all 6 slots.  Regards, 
Last night I installed x6 2GB (Dual Ranked) PC3-10600 ECC RDIMM's in to my T310 (w/ Xeon X3440), and it did not work.  Removing the RDIMM's from slot 5 and 6 resulted in the system working normally. All the RDIMM's are healthy, the ones pulled from 5 & 6, work in 3&4, not to mention this RAM was pulled from a functioning server to begin with. As I cruised the Technical Guidebook, I get lost. [URL] On page 36 - Table 9, it suggests x6 2GB 1333 RDIMM's is supported (PC3-10600 = DDR3-1333Mhz, right?) on page 38 - Table 12, it suggests by the *, that Dual Ranked RDIMMS are only supported in all three channels; if they are in 16GB or 32GB configuration (which neither is divisible by 6, so not sure how this applies) on page 40 - Table 8, is suggests 2GB RDIMM's are supported for 12GB using 6 RDIMM's Do I need a BIOS update?  I could use some clarification, and possibly might enjoy the functional theory behind why this isn't working.  
Power Edge T310 Memory Support