Plesk is blocking control panel due to "invalid license key" error after changing time/date on the server.

After time/date adjustment on the Server-> System Time page in Plesk CP, access to Plesk is  blocked with the following license error:

Error: The license key is invalid. In order to use the control panel, please, obtain and install a new fully featured license key. Your license key has expired. To continue using your control panel, purchase a non-expiring commercial license.

Cause

Clock adjustment settings on Server -> System Time page show year as YYYY+1, where YYYY - is the current year. So if Plesk admin user wants to change only minutes or timezone of the server he has to change year setting also, and if he does not, then  license would be reported as expired because of data on the server be set to the next year.

Resolution

Check data on the server using the 'date' command. If you find that current time is set to next year, please change system time back on the server with the command:

# date --set='-1 year'

This problem will be fixed in further Plesk versions.