[AX2012] Ax error "A user session on the server could not be created. Try to start the client again. If the problem continues contact Ax Administrator"

I checked the Event viewer and found that the log file was full:
Object Server 01:  The database reported (session 1 (-AOS-)): [Microsoft][SQL Server Native Client 10.0][SQL Server]The transaction log for database
'AXDatabase' is full due to 'LOG_BACKUP'. . The SQL statement was: "UPDATE SQLSYSTEMVARIABLES SET VALUE='34' WHERE PARM='SYSVARID'"

Solution:
Stop the AOS.
Shrink database log file and start the AOS.