I found zero hits for the VCS-1002 error for Extreme Networks (formerly Brocade) VDX line so this is my experience with it and how to fix it.
I had two VDX switches and wanted to form a VCS logical-chassis fabric. I knew their firmwares had to be the same version but was unsure how much needed to match: one switch had NOS 6.0.2b and the other 6.0.2f. I hoped that it was enough to match on the “6.0.2” part (short version: no). The switches never formed a logical-chassis fabric.
I finally realized how to check the logs and saw an error about the primary switch being unable to configure the secondary.
2018/04/30-12:55:39 [VCS-1002], 10559, SW/0 | Active, ERROR, VDX6740, Event: VCS cluster create, Coordinator IP: IP, VCS ID: 1, Status: VCS cluster failed to be created, Reason: Failed to configure all new locations.
I backed down the VCS level to fabric cluster and then a fabric formed. I still wanted the full thing however so opened a support case and after talking to the representative, discovered the versions must exactly match. I got the 6.0.2f firmware, upgraded the other switch, and logical-chassis fabric formed immediately (or as immediately as the slow switches can).
Some time later a third switch was added and this time it seamlessly joined the fabric once the VCS ID was updated.