When you use Veeam to backup a vCenter cluster that is running on vSphere 5.x VCSA, there is a chance you will get an error when trying to backup the VCSA it self. This only applies when you have Enable VMware tools quiescence in you backup job. One way to backup the VCSA is to make a separate job for the VCSA and uncheck “Enable VMware tools quiescence” in this job. Another way is to disable it from within the eg. “cluster backup job”.
First Edit the job containing the VCSA in the step called “Guest Processing” click the “Advanced” button.