Login prompts after changing network password

[jp32]

In our environment we require users to change their passwords every 90 days. We have one user that constantly receives the login prompts. The prompts are usually for our sharepoint/intranet homepage. I've already done the following steps but still no luck. Our user will be fine for about a day or two then the login prompts pop up again.

1. Click "Start" > "Settings" > "Control Panel"
2. Double click "User Accounts"
3. Click on the "Advanced" tab
4. In the "Passwords and .NET Passports" area click "Manage Passwords"
5. Remove everything there.

Also, delete everything IN this directory:
C:\Documents and Settings\YOURUSERNAME\Application Data\Microsoft\Credentials

and everything in this directory:

C:\Documents and Settings\YOURUSERNAME\Local Settings\Application Data\Microsoft\Credentials

Any suggestions??