ASP.NET Web Api DllImport (LoadLibrary) fails on IIS

[iacierno]

Hi,
I'm developping a Web API that needs to call an unmanaged DLL written in C++.

In debugging (IIS Express), I'm able to call the function within the DLL and LoadLibrary is loaded correctly with a Handle.
Problem comes when I deploy my Web Api to my local machine (IIS 8): It recognizes the path of the DLL, permissions are also set properly, but LoadLibrary fails bacause I get a IntPtr.Zero.

I used Marshal.GetLast Win32Error() to detect the error, but I get error Code 193, which seems to have nothing to do with LoadLibrary.


Here's my code:

 if (!Directory.Exists(PATH) && !File.Exists(PATH_DLL))
                    throw new Exception(string.Format("Dll not found: {0}.", PATH_DLL));

                //LoadLibrary
                hModule = DllInterop.LoadLibrary(PATH_DLL);
                IsLoaded = (hModule != IntPtr.Zero);
                if (!IsLoaded)
                {
                    int errno = Marshal.GetLastWin32Error();
                    throw new Exception(string.Format("Failed to load library. Fehler:{0}.", errno));
                }

I would be very grateful for your help. Thanks in advance!

[madankarmukta]

Use Debugger.Break( )

It has certainly to do with IIS_USERS Permissions set to the DLL_PATH.

else Fusion Log Viewers can also be used.

Hope this helps.

[iacierno]

Thanks for your reply!
I don't think it's because of permissions regarding DLL_PATH.
I tried if I'm able to access any other function in "kernel32.d ll" or even "user32.dll ".

[DllImport("kernel32.dll")]
public static extern bool Beep(int frequency, int duration);

[DllImport("user32.dll", CharSet = CharSet.Unicode)] 
public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);

But none of them is working on IIS. Debugging with Visual Studio works...
I even tried to change the identity of the application pool to "Local Filesystem", but without success.

Do you have any other suggestion?

[iacierno]

Thanks for your suggestion. I found the problem: in my c++ DLL I was calling MessageBoxes, which seems to represent a problem on production.

MessageBox from user32.dll and the Beep from kernel32.dll might not be loaded beacuse of permission set to the IIS running on session 0.