Member Avatar for David_87

Hello. Please help me to stop an Excel error message. Every time I try to open the file, I get this error: "The file is unknown".
Has anyone any experience in this and if so could you help point me in the right direction? How to repair Excel file?

Any help/advice would be appreciated.

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  • Latest Post Latest Post by rproffitt

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Following ’s report and the thread notes from and , a compact, safe checklist to diagnose "The file is unknown" Excel problems (work only from copies; test suspicious files in an isolated environment).

  • Make a copy and check the file size and timestamps. A 0‑byte file or very small file usually means corruption or an interrupted save.

  • Inspect the file header to detect its real format (open the copy in Notepad or use a quick PowerShell check). Common signatures: ZIP/PK (OpenXML .xlsx/.xlsm), OLE/CFBF (older .xls), plain text/CSV/HTML. Example PowerShell one‑liner to show the first 8 bytes in hex:

    [System.BitConverter]::ToString((Get-Content -Path "C:\path\to\file" -Encoding Byte -TotalCount 8))

  • If the header says PK, try renaming the file to .zip and examine the archive (an .xlsx is actually a ZIP of XML files). If it’s OLE/CFBF, Excel’s binary format may still be repairable.

  • Use Excel’s built‑in recovery: Open Excel → File → Open → select file → click the open button’s dropdown → choose “Open and Repair” → Repair (or Extract Data). If the extension doesn’t match the detected header, temporarily change the extension to the expected one and retry the repair.

  • If the file looks like text (CSV/HTML), import it via Excel’s text import tools rather than double‑clicking.

Extra notes: avoid running unknown macros or executables; scan the copy with up‑to‑date antivirus before opening; test in a VM/sandbox for risky files (echoing ’s isolation advice). If all attempts fail and recovery matters, capture the exact Excel version/OS, the full error text, the file size and the first 8 hex bytes (from the PowerShell one‑liner) when requesting further help — those details are the most useful for diagnosing header/format mismatches.

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Member Avatar for rproffitt

Read priors like

Why is your post almost exactly like theirs? Have you been working this issue in more than a few forums?

Member Avatar for happygeek

[waits for responses to spam bait telling us which crapware is best for repairing Excel files]

Member Avatar for David_87

Becuase it is my post. I did not find the solution. I was banned for my question!

Member Avatar for AssertNull

I want to say thank you for taking the time to share how to go about fixing this.

So it's fixed?

I did not find the solution.

Guess not. Therefore we can assume that if some helpful newbie posts the exact same "solution" that didn't work the last time, you'll immediately post that no one should use that lousy product that doesn't work at all, right?

Member Avatar for rproffitt

I can understand the ban. There are so many shills posting that question with a spam reply that moderators just ban or remove such a post today.

It's not like you can't google for repair tools. Find any that are "try before you buy." But given the rather nasty RANSOMWARE apps going around you know to try this only in a disposable PC.

PS. Added with edit. A rather new PC user had the file unknown problem. Turns out they didn't know to install Excel or such. I set them up with NINITE.COM, LibreOffice and they were able to open the spreadsheet. For free no less.

Edited by rproffitt because: Added PS.
Member Avatar for AssertNull

I got a little grouchy and cynical perhaps, OP. I too tend to default towards cynicism on these topics for the reasons RProffitt mentions. Thus, apologies if this is a real question.

But given the rather nasty RANSOMWARE apps going around you know to try this only in a disposable PC.

I'm not sure if you have to go that far. Virtual Machine seems ideal here.

But "The file is unknown" seems like an odd error message. Never seen that one in Excel, which of course doesn't mean it doesn't exist. But I would hope Excel would give you something a little more detailed to work with. Exact error message and circumstances are crucial.

commented: You're right. A Virtual Machine would do nicely. +11
Member Avatar for rproffitt

. After so many error messages and doing the moderator thing for years I find that some folk are translating from another language so they might be correct. This means folk shouldn't omit the original untranslated error message.

How to ask a question is an art too.

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