Can't preview text file attachments in Outlook

Question

Something is wrong with my preview handlers in Outlook.

When I receive an email with a .txt attachment*, if I click on it, I get this message in the preview pane:

This file cannot be previewed because of an error with the following previewer:

Windows TXT previewer

*_{This problem applies not only to .txt files, but to any file types that are associated with the prevhost.exe preview handler (e.g., .rtf,. .sql, .reg, .bat, etc)}

Following a suggestion from this post, I deleted the Windows TXT Previewer from the following registry folder (after backing it up, of course):

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\PreviewHandlers]

This fixed the problem with Outlook (instantly), but broke the Preview Handler in Windows Explorer. (The Preview Pane in Explorer now displays "No preview available"). Conversely, when I restored the registry key, it fixed the Windows Explorer previewer, but it broke the Outlook previewer again.

Other things I've tried without success:

• attaching prevhost.exe to the debugger in Visual Studio, but I don't have the source code and can't read assembly.
• running sfc /scannow
• Disabling the Windows TXT previewer in Outlook->Options->Trust Center->Settings->Attachment Handling->Previewers (this just displayed a new message in the preview pane: "previewer has been disabled" with a button to re-enable it, which simply restored the original error message.

Other suggestions??