Diagnosis
The thermostat is preventing your HVAC system from turning on again too soon after shutting off. This protects the compressor from damage.
How to Fix It
Wait. This is a protective lockout, not a malfunction. The thermostat will automatically reset after the required time passes, typically 5 minutes. Do not power cycle the thermostat to try and clear it. Let the system rest.
If That Didn't Work
If you get this error frequently without normal cycling, you may have a system issue. A failing relay on the furnace control board or a stuck contactor in the outdoor AC unit can cause rapid, false cycling. An HVAC tech needs to check the control voltage.
Heads Up
This lockout is a safety feature. Forcing the system to restart by cutting all power can damage the AC compressor, leading to a very expensive repair.