Unable to load DLL access is denied (exception from HRESULT: 0x80070005 (E_ACCESSDENIED))

Question

I'm consuming a 32-bit native DLL from a c# web service. Everything works fine locally in VS with IIS express. However when I deployed the site to a shared hosting provider (Server 2012 R2, IIS 7) the calls to the DLL (using platform invoke) generated an exception:
Unable to load DLL 'dll_name.dll': Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))
I asked the hosting provider to make sure my process is running in 32-bit mode and they assured me it is.Do I need to do anything special to use native DLLs? Do I have to register native modules with the server before they can be used? Anything to be set on
the server side to grant access to the DLL?
Thanks

Answer 1

Thanks for your reply.
Tech support tried the following:
Ran "tasklist /m Detection.dll" It didn't return any processes that would lock the dll.
Checked the permissions on the dll. The Network Service and app pool identity both had read/write/execute permissions. Just to make sure it wasn't permissions, they added IIS_IUSRS
with r/w/x. Still didn't work.
When this exception occurs, the exception.Message reads:
Unable to load DLL 'Detection.dll': Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))
However, the exception.HRESULT value is 0x80131524 which it seems to be DLL not found. I'm not sure why there's a difference.
I recompiled the DLL with the  DetectObject() function removed (See code snippet below), that didn't seem to make any difference (same error codes)
If I delete the DLL from the /bin folder, I get the following message:
Unable to load DLL 'Detection.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
The code that calls the DLL is as follows: 
public class DllCalls
[DllImport("kernel32.dll", SetLastError = true)]
public static extern bool SetDllDirectory(string lpPathName);
[DllImport("Detection.Dll")]
public static extern int DetectObject(IntPtr array, int Rows, int Cols, string BaseFolder);
public static class DetectionApis
public static int[] DetectRectangle(int[] LumaImage, int LumaStride, Rectangle Rect)
int DetPts = 0;
string DstDll = System.Web.HttpContext.Current.Server.MapPath("~/bin");
DllCalls.SetDllDirectory(DstDll);
/*=================================================
* Extract region of interest rectangle
*================================================*/
byte[] RoiRect = new byte[Rect.Width * Rect.Height];
ImagePixels.ExtractRectToBytes(LumaImage, LumaStride, Rect, ref RoiRect);
/*=================================================
* Pass array ByRef
*================================================*/
int ArraySize = RoiRect.Length;
byte OneByte = 0;
IntPtr buffer = Marshal.AllocCoTaskMem(Marshal.SizeOf(OneByte) * ArraySize);
Marshal.Copy(RoiRect, 0, buffer, RoiRect.Length);
try
string BaseFolder = System.Web.HttpContext.Current.Server.MapPath("~/cascades") + "\\";
DetPts = DllCalls.DetectObject(buffer, Rect.Height, Rect.Width, BaseFolder);
catch (Exception e)
LogFile.WriteLogStrg("DetectObject() caused an exception: " + e.Message + "HRESULT = " + e.HResult.ToString("X8"));
return (null);
int[] DetPoints = null;
if (DetPts == 8)
DetPoints = new int[DetPts * 2];
Marshal.Copy(buffer, DetPoints, 0, DetPts * 2);
Marshal.FreeCoTaskMem(buffer);
return (DetPoints);
The imported DLL function is as follows:
#ifdef __cplusplus
extern "C" {
#endif
__declspec(dllexport) int __stdcall DetectObject (int *CharLumaBuf, int Rows, int Cols, char *BaseFolder)
return(-100);
#ifdef __cplusplus
#endif
 Any ideas/suggestions?