It could be the PCs are using cached credentials which have expired. This
would point to the PCs not being able to find a DC. To test try changing the
user password on one of the affected PCs by the Change password option on the
Ctrl-Alt-Del screen.

Best Regards
Joe Dunn MCSE

"Ricky" wrote:

I don't know what's going on with 2 sites of my network once users outlook
keeps asking for domain/username and password when the clients opens the
outlook and then passed a few minutes asks again.

I've already check all outlook and exchange configuration and I don't know
what do...

I hope someone can help me!
Thanks