Hi,
As a troubleshooting process
1. stop all the sas services,
2. Take back up off old logs from the folllowing location 
    /sasconfig/Lev1/web/webappserver/sasserver12_1/logs/server.log
    /sasconfig/Lev1/web/Logs/Server12_1
3. Once backup of the logs is doneto other location(can save in your local system), try restarting the sas services
 
 
Regards
Jubi