What type of server script do you use? If OS script, check the permission of the script files.
check the log's - there should be some more info (admin console)
as user19752 mentioned: What kind of scripts?
No logs, kind of as expected as you can see in the screenshots it says ‘Running’ and next run Nov 27, 2015. That’s likely the date I moved to FMS14.
If I try to edit the schedule Admin give me the error, ‘No scripts are available for the specified account.'
Admin console defines the script as Type: ‘FileMaker Script’.
If I trigger the scripts from within FM database 1 seems to run as expected, one got 1 error about a user having in use or not having privilege.
Can you stop the running script using CLI or restarting server?
Here is same issue that you can't select script in file "No scripts are available for the specified account"
I also saw that in my installation (may be older than FMS14) but can't recall how it was fixed or not.
FileMaker Server uses the fmserver account to run scripts. Maybe the 12 installation used a custom account (or the other way around).
Did you use the default or use a different account during the 14 server setup? If so it's probably a rights issue.
Sometimes the management console is out to sync with reality. Scripts would say they where running when they weren't. Then it's time to just restart the whole machine. (But that was fmserver11 back in the day...)