Fix ERROR_UNSUPPORTED_COMPRESSION (0x0000026A) in Windows

The 30-Second Fix: Restart and Retry

This sounds too simple, but you wouldn't believe how many times I've seen this error vanish after a full reboot. The reason: Windows sometimes caches compressed file metadata or holds onto a corrupt section of memory. A clean restart clears all that.

1. Close any programs that are accessing the compressed file or folder.
2. Click Start > Power > Restart.
3. After Windows reloads, try opening your compressed file again.

What to expect: If the file opens without the error, you're done. If it doesn't — or if the error appears in a backup tool or system process — move to the next fix.

The 5-Minute Fix: Check Your Compression Tool

The error 0x0000026A specifically means Windows doesn't support the compression format. That often happens when you're using a third-party tool like 7-Zip, WinRAR, or WinZip, and it's either outdated or set to a format Windows can't handle natively.

Step 1: Update your compression software

I see this most often with 7-Zip. People download it once and never update it. 7-Zip 19.00 and older had issues with LZMA2 archives that newer versions handle fine.

• Open 7-Zip, click Help > About to see your version.
• If it's below 21.07, go to 7-zip.org and grab the latest.
• Install the update, reboot, then test your file.

For WinRAR: check Help > About. Version 6.00 or higher is fine. Lower than that, update from rarlab.com.

Step 2: Try a different extraction method

If your file is a .zip, .7z, .rar, or .tar.gz, the fastest test is to extract it using a different tool. Windows' built-in Zip utility is limited — it only handles standard .zip and .cab files. If your archive uses LZMA, BZip2, or PPMd compression, Windows will throw this error every time.

• Right-click the file, choose Open with > 7-Zip (or your installed tool).
• Try extracting directly from that tool instead of double-clicking.

What to expect: If the extraction works in the third-party tool but not in Windows Explorer, the file format is simply incompatible with Windows. That's not a bug — it's a limitation. You're done.

The 15+ Minute Fix: Repair or Convert the File

If you've updated your tools and still get the error, the file itself might be corrupt or encoded in a format that nothing on your system understands. Here's how to dig deeper.

Step 1: Check the file header

This is for the more technical crowd. Open Command Prompt as Administrator and use the certutil command to see the file's real signature. That tells you the actual compression format.

certutil -hashfile "C:\Path\To\YourFile.ext" MD5

That just gives you a hash. What you really want is the first few bytes of the file. You can use a hex editor like HxD (free) or even PowerShell:

Get-Content -Path "C:\Path\To\YourFile.ext" -Encoding Byte -TotalCount 16 | ForEach-Object { $_.ToString("X2") }

Compare the first 4 bytes against this short list:

If the header says LZMA or XZ and your tool is set to standard ZIP, the file was created with a different program. You'll need to convert it.

Step 2: Repair a corrupt archive

Corruption can cause the compression format to appear unsupported even when it's not. 7-Zip has a built-in repair function, but use it only as a last resort — it's not always successful.

• Open 7-Zip.
• Select your corrupt file.
• Click File > Open archive.
• If it opens, extract what you can. If it doesn't, click Tools > Repair archive.
• Choose Scan to let it rebuild the structure.

Alternative tool: PhotoRec — yes, it's for photos, but it recovers any file type by reading raw data regardless of the archive format. I've pulled files out of corrupted .7z archives with it. It's free, no install needed, runs from USB.

Step 3: Convert the file to a Windows-friendly format

If you have the original uncompressed files somewhere else, re-archive them using standard ZIP compression. In 7-Zip:

1. Select the files or folder you want to compress.
2. Right-click > 7-Zip > Add to archive.
3. In the Archive format dropdown, pick zip.
4. Under Compression level, choose Normal or Fast (not Ultra — that uses LZMA).
5. Click OK.

Now Windows can open it natively. If you're stuck with a single corrupt archive and no backup, try CPU-Z (unrelated name, different tool) for analyzing compression streams — that's an advanced recovery technique.

When Nothing Works

Sometimes the file is just toast. The compression format might be proprietary (like Microsoft's own Xpress or LZX used in some old CAB files) or the file header got overwritten. In those cases, your best bet is to:

• Ask the sender to re-save the file as a standard .zip.
• Use a file recovery service — but only if the data is critical.
• Check if the file is actually a renamed executable or image (sometimes people change .exe to .zip to bypass email filters).

I've personally seen this error happen twice with backup archives from a Synology NAS that used an old LZMA variant. The only fix was to restore from a different backup. So if you have other copies, use those.