From what I could dig out, FConversion is a part of the Visai Tamil suite. Unfortunately, I can't find any information regarding Windows compatibility about that product, but it could very well be completely incompatible with the latest version of Microsoft's operating system.
As far as options go, the one most likely to succeed is to roll back to an older version of Windows. If you would like to keep using Windows 10, you could try:
- Running the application with administrator privileges. (Right-click the executable, select Run as Administrator).
- Running the FConversion in compatibility mode with a previous Windows version. (Right-click the executable-->Properties-->Compatibility)
- Setting up a virtual machine with an older Windows version on it, the run the program using that virtual machine.