What type of backup are you running? And version of the software?

Also, that error may be related to the local repository database we manage. It's not clear the actual source, and the logs would probably point us in the right direction. Are you saying you submitted logs to Support? If so, are you working the case with them or has it been closed?

You can check Options - Repository and make sure the drive where the repository is located is not out of space (or low on space).

Have you made any security changes recently? Does the backup service account have access to the Repository location on those computers with the issue?

All machines are with the agent in version Build (7.2.1.49)

That agent version was just released. Were you using an agent version prior to this or are these fresh installs? If you used a prior agent, then did you have the same problem or did the issue start to occur when you moved to 7.2.1.49?

And please see the other questions in my previous post.

I performed the update of the agents and ran the backup again, it has been some time creating the VSS of the volume C:\.

I'm waiting but will probably return the same error.

This has probably already been resolved, but for someone coming along afterwards, we just had a similar issue when trying to access the Backup Storage tab. Our solution was to uninstall the agent (which is version 6.3.9.12), and to reinstall the same version. After the reinstallation, the issue was no longer present.
Hope this helps!