Excel, Access, external DB driver errors linked to this month’s patches

I’m seeing many reports, in various locations, about this month’s Windows security patches breaking custom programs that import and export Excel XLS files. Programs that have worked for years are suddenly, mysteriously, turning belly-up. The most common symptom is an error message that says “Unexpected error from external database driver” followed by a number.

There’s no mention of the error in any KB article that I can find, and it isn’t listed on the Fixes or workarounds for recent issues in Excel for Windows site. Either Microsoft isn't aware of the problem, or it isn't commenting on it.

On the Stack Overflow site, poster xMRi states:

The problem arises in fact due to a bug in the security updates. Currently I see no other solution than to uninstall the security patch or using another export format. Affected patches are:

KB4041681 — 2017-10 Security Monthly Quality Rollup for Windows 7 for x86-based Systems

KB4041678 — 2017-10 Security Only Quality Update for Windows Embedded Standard 7 for x64-based Systems

KB4041693 — 2017-10 Security Monthly Quality Rollup for Windows 8.1 for x86-based Systems

KB4041687 — 2017-10 Security Only Quality Update for Windows 8.1 for x86-based Systems

KB4041691 — 2017-10 Cumulative Update for Windows 10 Version 1607 and Windows Server 2016

KB4041676 — 2017-10 Cumulative Update for Windows 10 Version 1703

Solutions to the external database driver error

There are many proposed solutions. Two of them seem to work, at least for most of the people. The easiest (and most reliable) solution is to simply uninstall the appropriate October Windows update.

The other approach is a bit more complex — and hard to explain.

According to fred.schulz on the Technet forum, who credits a thread on the Embarcadero forum, some (or all) of those Windows updates install version 4.0.9801.1 of msexcl40.dll. (No explanation why a Windows security patch would install a new version of the Excel runtime, but, hey, this is Microsoft.) Apparently that’s at the core of the problem. Schulz’s solution:

1. Find prior version (4.0.9801.0) of msexcl40.dll.
2. Place in another directory. They suggest the application directory, but since in the next step you will modify registry to point to this older version, it can probably go anywhere.
3. Update registry key HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Jet\4.0\Engines\Excel\win32 to point to the location from step 2.

Thanks to reader RD.

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