I have Nimbles (CS500, f/w: 3.7x) integrated into my VB&R server (v9.5 U2) & have this issue as well. Now, though I get this error, I have my jobs configured to 'retry' after a failure up to 3 times. At the 2nd attempt to b/u my VMs, the jobs will run successfully. This error occurs occasionally... not for all my b/u jobs, and not consistently with the same b/u job. It's a sporadic/occasional issue, but as mentioned... will eventually run successfully. Anyone get an answer from Veeam support? I'm going to open a case as well. Curious to hear about others' experience & solution on this issue.
Sr. Systems Engineer
VMware vExpert 2011-17
Cisco CCENT, VCAP5-DCA, VCP-DCV/DT/Cloud