"Debugging and troubleshooting", "List of MyChat Client errors", "Ошибка #0333".
 
Error

Error #0333: impossible to make a call in a conference, the mixer is disabled on the server
 

Error description

The special media mixer (C:\ProgramData\MyChat Server\mixer\mixer.exe) was disabled or not running on the computer with the running MyChat Server. Calls in conferences does not work.

 
Problem solution

Perhaps, you are not launching the mixer on purpose (mcserv.exe /MIXER=NO), it has been removed from memory manually or has crashed due to some error. Usually, restarting MyChat Server solves the problem.