I had that access problem occur frequently and I found a fix. Since then it has not occurred again. I had to SAVE the admin login information in the client computer using this Windows feature:
To add a password to your Windows vault
Open User Accounts by clicking the Start button Picture of the Start button, clicking Control Panel, clicking User Accounts and Family Safety (or clicking User Accounts, if you are connected to a network domain), and then clicking User Accounts.
In the left pane, click Manage your credentials.
Click Add a Windows credential.
In the Internet or network address box, type the name of the computer on the network that you want to access. This can be the NetBIOS name (example: server1) or DNS name (example: server1.fabrikam.com).
In the User name and Password boxes, type the user name and password that you use for that computer or website, and then click OK.
