"Debugging and troubleshooting", "List of MyChat Client errors", "Error #0300".
 
Error

Error #0300: incorrect ID (XX) of the common user group
 

Error description

It turned out, that when requesting a user list from a common group, the group number specified incorrectly or does not exist.

 
Problem solution

If you work with MyChat via API or directly using an open network protocol, change the transferred data. Do not confuse a user group with contact groups and rights group, because they are completely different things.