This can happen for a couple reasons.. The first being that the service for whatever reason has been interrupted or there are duplicate software packages installed for the same device and the server is unable to determine which one is take control..
First I would restart the Dserver service, Wavelink Avalanche Agent. If the issue continues to happen, i would then check your software profiles for a duplicate package for the devices that receive this error.. if there are duplicates, you will need to disable one of the duplicates and sync the dservers to the change..
If after all this and the issue still persists, contact customer support for further troubleshooting. When contacting support, it would be handy to have the Avalanche.log file handy, as this will be requested when troubleshooting the issue..