If a user has turned off Remote Control via their Agent Menu, you can re-enable it via command line.
For 32-bit systems:
net stop "Kaseya Agent"
reg delete HKLM\SOFTWARE\Kaseya\Agent\(agent identifier) /v EnableRemoteControl /f
net start "Kaseya Agent"
For 64-bit systems:
net stop "Kaseya Agent"
reg delete HKLM\SOFTWARE\Wow6432Node\Kaseya\Agent\(agent identifier) /v EnableRemoteControl /f
net start "Kaseya Agent"