All, we had our QA research the issue, and the change in behavior appears to be caused by a bug fixed in v10.
In previous releases, "Require
successful application-aware processing" option was quietly ignored for Linux VMs without credentials assigned. This is a bug, because this can potentially result in unrecoverable backup without the user knowing.
In v10, you will see the above-mentioned error in such situations. This is now consistent with how it always worked for Windows VMs.
You have two options to get rid of the error, both of which are already captured above:
1. Specify the missing credentials for the Linux VM in question.
2. Change the application-aware processing setting to a less strict one in the advanced settings
on the Guest Processing step of the job wizard. Or, disable it completely for the specific VM only.