Have you tried to do remote configusing the DTK Director, or using the SCA out of the SDK? Your issue sounds like a setup issue in the SCS, so I'd try to use a different method to do remote config so thatyou can see whetheryou've got a firmware issue or a tool issue.
On the system in question, I'd like you to reset the system to factory defaults to ensure the MEBx password is truly "admin". If you are unfamiliar with doing this, here is how... open the case, on a dc7700 there should be a small yellow button with "CMOS" written near it (it will be near the back next to the SATA connectors). Press and hold this button for 15 to 20 seconds. Put the cover back on and rerun your provisioning test with out modifying the MEBx password. Let us know the results.
FYI - I was on the HP site, they have a newer ME Firmware image available. If the above does not work, you might want to try the newer image. If you go this route, please perform the same CMOS reset defined above after finishing the Firmware upgrade.
I have tried reseting the BIOS to factory default, and upgrading the BIOS to the newest version i.e. 188.8.131.523 already but without luck. :(
This is odd. Are you using the latest version of SCS Light (tech release 3)? Also, have you been able to run Roger's suggestion? (remote provision the system with something other than SCS Light). Finally, you mentioned ealier other systems working properly... are they later versions of Intel AMT and/or different OEM systems?
I am using SCS Light Tech release 3 from http://software.intel.com/en-us/articles/download-the-intel-AMT-SCS-technology-preview/ . Other systems are from the same OEM, and AMT versions are 3.x and 5.x. I however did not run any other tool for remote provisioning yet.