It looks like it is known problem:
Mar 3, 2010
Motherboard DP55SB with I5-650 CPU
Sep 20, 2010
DP55SB Mother board gives E6 error
Another board, but the same symptoms
Jul 11, 2010
DP55WG not displaying
Oct 2, 2010
Does DP55SB work with Clarkdale processors?
I have the same problem.
DP55SB + i3-540 + ATI 5770 = Eb POST code
I have tried this combination
DP55SB + i3-540 + ATI 5450 = Eb POST code
It is interesting, that with old ATI card everething OK
DP55SB + i3-540 + ATI Radeon X700 = ok
I wrote to technical support, but there is no answer.
DP55KG: i3-540 same E6 error and no Bios or video even with latest bios version 5531 issued May 21, 2010 and am running windows 7 64 bit.
i3-540 + ati 5670 = E6 no video and very frustrating experience to have a supposidly supported CPU that has this common video compatibility issue.
i3-540 + ati 3450 = boots fine
i5-750 + ati 5670 = boots fine
Maybe there is an issue with the express bios update not working correctly. Did not try the Recovery Bios Update as already using version 5531.
Went out and bought a Gigabyte MB during this testing and i3-540 + ati 5670 works fine. Frustrating experience and we paid a premium price only to discover Intel no longer supports its own products. Diligently searched this Intel board using goolge and enter "site:intel.com E6" provides far more search results.