C# uninstall app using msiexec process

See more:

C#

Windows

installer

I have a c# exe that is supposed to unistall another app. the code is as follows:

private void removeApp()
{
    ustAssembly = @"c:\path\tosome\file.exe"
    Assembly ustAsm = Assembly.LoadFrom(ustAssembly);
    string appGUID = "{" + ustAsm.GetType().GUID.ToString() + "}";
    string args = @"/x " + appGUID;
    Process p = new Process();
    p.StartInfo.FileName = "msiexec.exe";
    p.StartInfo.Arguments = args;
    p.StartInfo.UseShellExecute = true;
    p.Start();
    p.WaitForExit();
}

When i run this exe, i get the following message:
"This action is only valid for products that are currently installed"

Just to note: I could have sworn it worked previously but, at my job they removed admin rights to all client machines and incorporated viewfinity to control what users/apps can do on a computer.

I went through a long exercise with a member of our viewfinity team to create policies for this app to work and he even went as far as granting me admin rights to the test machine but, its still not working.

I know this target app that i want to uninstall is in fact already installed on the test computer.
Any clue as to why i'm getting this message? Could it still be a rights issue?
Any help would be appreciated.