You initially posted in the phpVMS v7 Support forum. I moved your post here.
Does he have .NET 4.0 installed?
Does he have FSUIPC installed for his specific sim version?
Is he running kACARS_Free as Admin?
Are you able to connect to your site with kACARS_Free?
If the above doesn't work, he may have a corrupt .NET install and will need to reinstall.
If that doesn't work, maybe try installing .NET 3.5
You indicated you require kACARS_Free 1.0.1.1 (there is no 1.0.11) - is your site using 'http' or 'https'?
'https' requires kACARS_Free 1.0.1.5 and supports FS9, FSX, P3D, MSFS and XP - requires use of FSUIPC or XPUIPC (sim specific)