Jill, I'll see if I can get someone to help you.
It’s possible something may have changed in your managed passwords.
Go to Control Panel->User Accounts->Advanced tab-> Click Managed Passwords button.
Here there is a list of Addresses / User credentials stored for use by different applications. Verify that there is an entry that matches the exact address of your Exchange server.
I removed the settings that had been added and that resolved my problem. Thanks for your help!