Try and reset your Simtraffic by opening a sample file and running it. Then go back and open your file and run Simtraffic again. 

If this does not work. Please contact support and create a ticket. 

Let’s try to reopen using a sample file -
1.            Close the program
2.            Reboot machine
3.            Go to C:\Users\Public\Documents\Trafficware\Synchro 10\Sample Files
4.            Locate a sample file [.syn] and right click to ‘open with…’ Synchro11.