ESXi 5.5U2 - Domainlogin problems SSO

Hi guys,

last week i set up our new esxi server.

Following problem:

the users can only login with intern.xxx.de\User1.User1

Normally it should work with the short name of the Domain: XXX\user1.user1

If the user types the short name  xxx\user1.user1 the credentials work...

So our users actually can't use single sign on.

any ideas to fix the problem?

thanks!