Target a newer version of the .NET framework.

The application targets .NET 2.sth, which makes it usable under the 2.x/3.x branch.

Windows 7 was the last OS version to ship with .NET 3.5, newer version ship with 4.x by default and although installing older versions is supported it's not preferable.

Have you evaluated if your program can run in under .NET 4.x without retargeting? Try to add a configuration file following this at least: https://msdn.microsoft.com/en-us/library/w4atty68%28v=vs.110%29.aspx