Today, we P2V one vCenter Server, I re-added identify source for some reason, I didn’t modified any existing domain group and ACL.
After a while I got a interesting case. User reported they got “No permission to login to vCenter Server 5.1 by vSphere Client”.
I looked into the vpxa.log of vCenter Server, it show that:

2013-05-01T11:08:01.399-05:00 [09108 error '[SSO]' opID=6e704a51] [UserDirectorySso] AcquireToken InvalidCredentialsException: Authentication failed: Authentication failed

2013-05-01T11:08:01.399-05:00 [08644 error 'authvpxdUser' opID=5469f71e] Failed to authenticate user <xxxx>

I was not 100% sure that log related to the real problem. but that’s indicated it should be something related to authentication components.
After compared working SSO with the fault SSO, I noticed Domain Alias was blank on fault SSO:

Then I added a domain group on fault vCenter Server and compared the group with working vCenter Server, it’s shows format different, just like that:
Working SSO – CONTOSOTEST-GROUP
Fault SSO – CONTOSO.COMTEST-GROUP

Okay…now I know why user logging got fault. The identify source configured Domain Alias before I removed it on fault SSO, then I added identify source without Domain Alias, and thenvCenter Server used Domain name as default prefix of domain group, it lead to original domain groups format ( CONTOSOxxxx ) cannot be identified by SSO.

So I deleted the identify source and added a same source with Domain alias, problem fixed…