Issue:
A Veeam Proxy VM halted during a back up run and powering back on was unsuccessful
Troubleshooting
When trying to restart I was presented with the following error and the VM failed to start
File system specific implementation of LookupAndOpen[file] failed
Solution
Upon further investigation the Veeam Proxy had a Hot-Added disk still attached. I removed this disk via Edit Settings . We do not want to delete the files so ensure you DO NOT select "Delete files from datastore"), The VM then powered up.