I noticed that my Exchange 2010 datastores stopped being backed up, so I checked and saw that BE was no longer able to authenticate. I'm not sure why this would happen now when it was working fine recently, and we haven't upgraded Exchange or BE or anything major like that.
I am able to log into OWA using the "buexe" account and it is able to send/recieve emails. I checked the password and BE has the correct password. Also when I ran the BE support tool, the only issue it said was that the backup account was hidden in the Global Address Book (GAL), but it is not hidden.
When I test the credentials, it just says communications failure.
Please check if you are able to see the Exchange Information Store in the selection list of your current job or in the new selection list.
In the Resource credentials you may get the error about the Communication failure when the resource is no more seen in the selection list but it was selected when it was seen previously.