backup to server share fails credentials, but was working before windows reinstall

Had ATIH 2011 working on this new W7 system but had to reinstall Windows for other reasons. Now when I try and open the server tree to select a shared folder it asks me for credentials but won't accept any credentials, even domain administrator... so unable to backup to the exact folder that was working before...
trying to use "\\myserver\myshare" as the url... I read the KB article about this but it doesn't work.

Any suggestions would be appreciated. Prefer not to use the dreaded script drive mapping hack, that proved unreliable on another pc I had problems with.