An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full

Challenge

After installing Windows April update KB4015553 Veeam jobs and services fail at different operations with:
 

"An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full"

Cause

This particular update (and all consequent rollups that include it) causes the system to run out of free RPC ports when there are failed iSCSI connections.

Solution

Repairing or removing unsuccessful iSCSI connections , followed by the server reboot, was found to fix the issue. If removing unused iSCSI connections remove any targets from the ‘Favorite Targets’ tab that are associated with these connections” as they may be reconnected after reboot.”

More Information

https://social.technet.microsoft.com/Forums/SharePoint/en-US/492f62ce-aec8-4777-98f0-0c9dbf302954/problem-with-kb4015553?forum=winserverwsus