Hi, you set this in your meeting policy.
Go to OCS MMC -->Forest-->properties-->Global Properties
Open the Meetings tab.
See what policy is selected in the drop down. If you have a policy selected, view the details and how many users are allowed.
If you have "enforce per user" check to see what policy the users who are trying to start LM have. Then check the details in the meetings tab (as described above) to see what their policy allows.
Regards,
Matt