FIX: "Unable to initialize DAO/Jet db engine" Error (168004)

SYMPTOMS

When you run a Visual C++ version 4.2 or 4.2b application on a machine that has the 4.21.7022 version of the MFC DLL (MFC42.DLL), the following message appears when you try to use MFC DAO classes:

Unable to initialize DAO/Jet db engine

CAUSE

Version 4.21.7022 of the MFC DLL (MFC42.DLL), which comes with Visual C++ 5.0, always incorrectly tries to use DAO 3.5. Visual C++ 4.2 applications use DAO 3.0 and, therefore, DAO 3.0 is installed rather than DAO 3.5. When MFC tries to load DAO 3.5 and it is not there, the error message shown above appears.

RESOLUTION

Visual C++ applications that are statically linked with MFC do not use the MFC42.DLL and do not see the problem. Also, the MFC DLL (MFC42.DLL) that comes with Visual C++ 4.2 can be placed in the directory of the application so that it is used, rather than the newer MFC DLL.

It is possible to fix the problem by installing DAO 3.5 on the machine as well. However, keep in mind that this means you will be using a new Jet database engine, which may introduce new problems with the application that was tested using DAO 3.0.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Visual Studio 97 Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see the following article in the Microsoft Knowledge Base:

170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

You can see the bug with the MFC42.DLL by looking in the DAOCORE.CPP file included with Visual C++ 5.0. In several places in the file you can see the following code:

      // Determine whether to use DAO 3.5 or 3.0
      // Use DAO 3.0 if DLL build and not
      // built with MFC 4.21 or later
      BOOL bUseDao30 = FALSE;

   #ifdef _AFXDLL
      AFX_MODULE_STATE* pModuleState = AfxGetModuleState();
      if (pModuleState->m_dwVersion < 421)
         bUseDao30 = TRUE;
   #endif // _AFXDLL

Notice that the version checking is incorrect. The version is checked against '421' instead of '0x0421'. This means that bUseDao30 will always be FALSE and this causes DAO 3.5 to be used.