BadImageFormatException when impersonating user

Question

Im trying to impersonate a user from a windows forms application through the following code:

public void Impersonate()
{
    //elevate privileges before doing file copy to handle domain security
    WindowsImpersonationContext impersonationContext = null;
    IntPtr userHandle = IntPtr.Zero;
    const int LOGON32_PROVIDER_DEFAULT = 0;
    const int LOGON32_LOGON_INTERACTIVE = 2;
    string domain = ConfigurationManager.AppSettings["ImpersonationDomain"];
    string user = ConfigurationManager.AppSettings["ImpersonationUser"];
    string password = ConfigurationManager.AppSettings["ImpersonationPassword"];

    try
    {
        // if domain name was blank, assume local machine
        if (domain == "")
            domain = System.Environment.MachineName;

        // Call LogonUser to get a token for the user
        bool loggedOn = LogonUser(user,
                                    domain,
                                    password,
                                    LOGON32_LOGON_INTERACTIVE,
                                    LOGON32_PROVIDER_DEFAULT,
                                    ref userHandle);

        if (!loggedOn)return;

        // Begin impersonating the user
        impersonationContext = WindowsIdentity.Impersonate(userHandle);

        PrintReceipt();
    }
    catch (Exception ex)
    {
        MessageBox.Show("Exception impersonating user: " + ex.Message);
    }
    finally
    {
        // Clean up
        if (impersonationContext != null)
        {
            impersonationContext.Undo();
        }

        if (userHandle != IntPtr.Zero)
        {
            CloseHandle(userHandle);
        }
    }
}

The program is started through a shortcut pointing to a network share and the machine is running Windows7 32 bits.

But the program is throwing a BadImageFormatException on the line:

impersonationContext = WindowsIdentity.Impersonate(userHandle);

The exact same code does work from a console application and I've tried compiling the exe as 'Any CPU' and x86.

Im out of clues, does anyone know what can be done?