Please check these base checks from draft technote, if all looks good -
1. Check the status of the Media Server and VMGR is up and running by Sametime System Console.
2. Make sure IP addresses of VMGR and VMCU had been added to Trusted Servers of Sametime Community Server.
3. Confirm that for example vmgr.acme.com can be addressed from DNS.
4. Confirm that the following ports are being listened
5. Check the status of the IBM Sametime Video MCU Server from command line
Log in to the Sametime Video MCU Server as root.
Run this command:
service soft_mcu status
The server should display this message: soft mcu is up.
6. Confirm that the SolidDB service was started and is still running before starting the VMGR
7. Confirm that there are no Firewall blocking traffic between the VMGR and MCU
Also there is another technote worth to check -