sys(3) is handy when you are creating files named TMPxxxx and making sure you clean up afterwards but 2015 seems much more reliable. If you are using either I would make sure you are doing some cleaning up before you run the code as well as in it. These tmp files linger if you have a program crash/dont delete them 'always'. You then get juplicated file names with sys(3) (never had one with sys(2015) but that's no guarentee).

As to it never happening before, if you are cleaning the tmp files up it could just be that you have only just rebuilt that exe/dll/app despite the rest of the code being updated.

Regards