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Q199707: PRB: Some VB 5.0 Programs Do Not Run on Multiprocessor PCs

Article: Q199707
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:5.0
Operating System(s): 
Keyword(s): kbDLL kbKernBase kbVBp500
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Professional Edition for Windows, version 5.0 
- Microsoft Visual Basic Enterprise Edition for Windows, version 5.0 
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SYMPTOMS
========

If a Visual Basic 5.0 application attempts to load a 32-bit generic thunking
DLL, it might not run properly on a multiprocessor computer.

The term "32-bit generic thunking DLL" describes any 32-bit DLL that links with
WOW32.DLL to provide 16-bit code with access to 32-bit code. This type of DLL is
loaded by a 16-bit program through the LoadLibraryEx32W() API.

CAUSE
=====

For a 32-bit program to map a 32-bit generic thunking DLL into its address
space, you must also map the Windows NT Virtual DOS Machine (NTVDM.EXE) into the
address space. The Visual Basic 5.0 Runtime Library, MSVBVM50.DLL, collides with
NTVDM.EXE. Both MSVBVM50.DLL and NTVDM.EXE are based at 0x0F000000.

On a uniprocessor computer, the operating system successfully relocates NTVDM.EXE
and the program runs correctly. However, on a multiprocessor computer, NTVDM.EXE
cannot be relocated. For additional information, please see the following
article in the Microsoft Knowledge Base:

  Q199671 Relocation of NTVDM.EXE fails on multiprocessor machines

RESOLUTION
==========

A 32-bit generic thunking DLL should be loaded by a 16-bit program only. The
loading of a 32-bit thunking DLL into the address space of a 32-bit process is
unsupported.


STATUS
======

This behavior is by design.

MORE INFORMATION
================

When a Visual Basic 5.0 application makes a call to a function in a 32-bit
generic thunking DLL on a multiprocessor computer, the call fails. A query of
Err.LastDllError returns the error code 998 "Invalid access to memory location"
(ERROR_NOACCESS).

Additional query words:

======================================================================
Keywords          : kbDLL kbKernBase kbVBp500 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVBA500 kbVB500
Version           : WINDOWS:5.0
Issue type        : kbprb

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