I've found some programs I made works perfectly on Windows 7 64bit, but when I close them a window appear saying that "This program may need administrator privileges."* allowing me to restart the application as administrator or label that program with a "This program works perfectly".
"This program
might require administrator privilege".
Windows treats a process as legacy if it’s 32-bit (versus 64-bit), is not running with administrative rights, and does not have a manifest file indicating that it was written for this version of Windows.
And your app is probably being detected as a setup. The Program Compatability Assistant is probably looking for changes of the sort an installer would make, and not seeing them, and is assuming that you were trying to run a setup that is rejecting the current version of windows or needs some sort of compatability fix to work.
As mentioned above, use the manifest.