Sacado de XDA:
Found the problem to be (according to the online community) to be from a DLL-bug now fixed by Google (in 2.3) but not pushed out by for instance Sony Ericsson to our phones yet.
Workaround (for mainly hosted Exchange like MS Online Services)
Logg on to Office Live Meeting, at the very top your SAM Account name is located.
(they change @ for _ ----and there is a max 20 chars)
This makes the SETTINGS:
Domain: red002 (or whatever your on)
Username: first.lastname_DOMAI (remember MAX 20 chars)
Password: *************
Server: red002.mail.emea.microsoftonline.com