So I Googled this and it seems there is very little information out there, but I am hoping someone out there might have the answer because most people just say "check the HCL list" or "update your drivers", etc but these are pre-packaged responses. I am hoping someone else has seen this problem and actually resolved it. 
I am basically running ESXi 5.1 on an HP Proliant DL380 G6 and when I booted ESXi just hung on "Deltadisk loaded successfully".
Then I hit Alt-F12 and I can see an error stating:
- ScsiDeviceIO: 6356 Could not detect setting for sitpua for device naa.XXXXX
Basically a long number sequence at the end, but this machine worked with 5.0 and now I am seeing this after I upgraded to 5.1.