Test 4 is really your only valid test. If the memory doesn't work alone in slot 1, then there is a problem. The memory seems to be Fully Buffered (required) and other specs seem to be in order, so I'm not sure why it's not working. Did you update the BIOS before installing the new RAM? Did you also update the ESM/BMC? You might try clearing the NVRAM using the jumpers on the motherboard. I would assume, based on the available information, as unlikely is it sounds, that the new memory is mislabeled or bad.
Amazon Product Link New Ram Old Ram I have a PE2950 II with 4 x 2GB (HYMP525F72CP4N3-Y5AB-T) installed and purchased 4 x 4GB (HYMP151F72CP4N3-Y5AC-C).  Based on what I have seen error message E2011 seems to common when installing UDIMMs however I believe the 4GB sticks I bought are Fully Buffered RDIMMs.  I have tried the following configurations and all display the same "E2011 Memory Config Err" on the lcd.  I have updated to the latest BIOS 2.7.0  Anyone have any thoughts about what is causing the RAM to not be recognized?  Was I wrong about compatibility?  Or any suggestions on what RAM would work? Original Placement  of ram  1) Existing RAM + New RAM 2) New Ram instead of existing 3) New Ram in slots based on the manual 4) Single Stick in SLOT 1
PE2950 II - E2011 Memory Config Err