Why would some DLL functions fail on 64-bit Windows?

Question

I'm trying to run some LotusScript code (very similar to Visual Basic) in Lotus Domino on Windows servers.
The code calls some Windows API functions, and works fine on 32-bit Windows 2003 servers, but doesn't work on the one 64-bit server we've tried it on.

Here's one of our external function declarations:

Declare Function FindExecutable Lib "shell32.dll" Alias "FindExecutableA" _
(Byval lpFile As String, Byval lpDirectory As String, Byval lpResult As String) As Long

When trying to call that function, LotusScript produces the error message "External function not found".
I have tried both removing the Alias from the declaration, and changing the alias to "FindExecutable" with the same result.

I have also:
- For comparison, tried calling the GetForegroundWindow function in user32.dll - this works.
- Used the Dir function to confirm that shell32 exists with the path "c:\windows\syswow64\shell32.dll", then...
- Changed the Lib in the declaration to the dll's full path - this produces "Error in loading DLL" when calling the function.

Is there anything that must be done differently when calling shell32 functions on a 64-bit server?
Any other reason why the function call would fail on one particular server?

Answer 1

My guess is that the As Long might be the culprit here - it probably is a bit integer on 32 bit and 64 bit on 64 bit...

Answer 2

Did you try using "Declare Function FindExecutable Lib "shell32.dll" Alias "FindExecutableW" "

Answer 3

The program executing that script, is that a 64-bit application? If that's the case it is possible that this application cannot load 32-bit DLLs. (That would be the second problem)

To track down the first problem, load shell32.dll explicitly using LoadLibrary (don't use the full path!) and then use GetModuleFileName to get the full file name loaded. There can be all kinds of things responsible for messing with DLL paths. (WOW layer, UAC, path variable, ...)

If that actually works, you can try using Dependency Walker to see if FindExecutable is exported, but I think you'll run into problems before that.