Outlook 2010 issues with exchange 2003

I'm one more with exactly the issue, My environment is: exchange 2003, work station with windows 7 x64, which so far is not a difference with a x86 having the same issue and outlook 2010.

so error sending to some NOT to all addresses is: Unknown Error. Error is [0x80040900-0x80040900-0x0003ee

But there is something weired.... I have the exchange WEB interface up so if I send to the same address where outlook 2010 fails, the web interface works perfectly.

Any Idea ???