Question

My VBA code can’t access to my DLL in the C:\Windows\System32 folder on Windows 7 64bit and Word 2010 32bit.

Private Declare Function my_func Lib "mydll.dll" (ByVal param As String) As Long

Public Sub MyFuncTest
  n = my_func("a")
End

I copied mydll.dll into C:\Windows\System32 and called MyFuncTest but got an error message like “Error 53: ‘mydll.dll’ not found”.

However, I changed the declaration in code to:

Private Declare Function my_func Lib "C:\Users\myname\Documents\mydll.dll" (ByVal param As String) As Long

then I copied mydll.dll into C:\Users\myname\Documents, my account’s Documents folder, and MyFuncTest successfully executed.

Changing “mydll.dll” to “C:\Windows\System32\mydll.dll” in the declaration did not work. And I tried accessing C:\Windows\System32\mydll.dll with FileSystemObject#FileExists method on the same VBA environment, but it returned False (not found).

There was no problem on Windows XP and Word 2003.

Can anyone help?

Answer 1

This is a 32 bit DLL and a 32 bit process running in the WOW64 emulator on 64 bit Windows. File redirection is in play and so when a 32 bit process looks in system32 it is actually redirected to the 32 bit system directory SysWOW64.

The simple and quick solution is to move the DLL to C:\Windows\SysWOW64. However, as Cody Gray points out in a comment, it is not recommended for you to place application DLLs in the system directory. Normal practice is to place the DLLs in your application folder in the program files directory and make sure that folder is in the DLL search path when the DLL needs to be loaded.