MSSIPOTF_E_NOT_OPENTYPE (0x80097012) Fix

You're trying to install a font—maybe a nice sans-serif for a client's branding kit, or a custom icon font for a web project—and Windows spits back MSSIPOTF_E_NOT_OPENTYPE (0x80097012) with that cheery message: "The file is not an OpenType file." But you know damn well it's a .ttf or .otf file. I've seen this exact error when a client downloaded a font from a free site that had a corrupted zip file. The font file itself was fine—until their browser or unzip tool mangled the header bytes.

The root cause is simple: Windows checks the file's internal signature to confirm it's a valid OpenType or TrueType font. If the first few bytes look wrong—missing the OTTO or true or 1 magic numbers—you get this error. It's not your system being broken. It's the file being corrupt, incomplete, or misnamed (e.g., someone renamed a .png to .ttf).

How to Fix It

1. Re-download the font from a trusted source. Go back to the original site—Google Fonts, Adobe Fonts, or the font foundry's own page. Don't use third-party aggregators. Last week I had a client who grabbed a font from "dafont.biz" (not the real site) and every file was a renamed HTML page. You're better off downloading directly from the designer.
2. Check the file extension. Right-click the file, go to Properties, and look at "Type of file." It should say "OpenType Font File" or "TrueType Font File." If it says anything else—like "WinRAR archive" or "PNG image"—the file is mislabeled. Renaming it won't fix the internal data.
3. Unzip properly. If the font came in a .zip, extract it before trying to install. Don't double-click from inside the zip viewer. Use 7-Zip or Windows built-in extractor. One time I saw a font that had been double-extracted—inside the zip was another zip. The extracted file was an empty folder.
4. Install manually. Instead of double-clicking and hitting "Install," right-click the font file and select "Install for all users" if available. Or copy the file to C:\Windows\Fonts (you'll need admin rights). That bypasses some Windows validation quirks.
5. Clear the font cache (if it still fails). Press Win + R, type services.msc, find "Windows Font Cache Service," stop it. Then delete all files in C:\Windows\ServiceProfiles\LocalService\AppData\Local\FontCache. Restart the service. This forces Windows to rebuild its font registration. Use this only if the first four steps didn't work—it's heavy.

Still Not Working?

If you've done all the above and the error persists, the font file is genuinely broken. Some free font conversion tools produce malformed OpenType files that lack the correct table structure. Try finding a different version of the same font—maybe a .woff2 from a web font kit and convert it using a reliable tool like Transfonter. Or contact the font designer directly. I've had to email foundries more times than I like to admit—most will send you a clean copy.

One last thing: if you're on Windows 10 or 11, check that the file isn't blocked. Right-click, go to Properties, and under the General tab, if you see "This file came from another computer and might be blocked," tick "Unblock" and hit Apply. That alone solved it for a client who couldn't install a .otf font from their Dropbox download.