I recently was investigating an issue where backup jobs in vRanger failed for all VMs with the following error message:
An internal error occurred during execution, please contact Quest support if the error persists. Error Message: <VM>'s host could not be identified
This appears to be an inventory issue between vRanger and the vCenter server which was caused by the VMware VirtualCenter Server service not responding and requiring a restart prior to the jobs being invoked.
The above issue may be resolved by performing the following from the vRanger server:
1) Stop the vRanger API and FLR services.
2) Restart the vRanger service.
3) Start the vRanger API service.
4) Start the vRanger FLR service.
After performing the above I was able to successfully run a backup job which had previously failed.
Deans Blog 