[HUB] Error in Plesk: The number of resources exceeds the limit defined by your license

Symptoms

I get error:

The number of resources exceeds the limit defined by your license

or

The amount of currently used resources overrides the limits defined by your license.

Cause

You might be getting this error due to different reasons.

Resolution

1. your license allows hosting only 30/10/5 sites . See this article for resolution steps: 
   #214526305 Unable to activate Plesk: The number of websites hosted on the server exceeds the limits defined by your license
   
   

2. registry.xml file is corrupted . See this article for resolution steps: 
   #213923525 Unable to access/activate Plesk: The license key is invalid. In order to use the Panel, you need to obtain and install a new valid license key
   
   
3. Error is shown after upgrade to Plesk 12. If you use Plesk lease license, refer to article:
   #213923525 Plesk 12 key is invalid: the number of resources exceeds the limit defined by your license