Cannot open file ....xlsx because the file format or file extension is not valid.

I have already looked at previous posts, but cannot find any possible fixes.

Starting from yesterday, suddenly we are getting more and more of our users with this issue. Its not all files, but the ones they use frequently. When attempting to open:

"Cannot open file ....xlsx because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file"

What was tried and didnt work

Update/reinstall Box
Clear Box’s cache
Signout > re-sign in o365
Signout > re-sign in Box

Laptop restart
Box restart
Installing Box Tools (kinda)
o365 repair

Things to note

For some files, there is a sync issue on the Box App (network, but connectivity is fine for everything else)
When attempting to copy and paste the 'corrupted' file, I get
"Cant read from the source file or disk"

The only thing that worked for me so far:

Open the file via Box online > download > replace the 'corrupted' file and that works fine..... until the next day.

Is anyone else experiencing this? Its really frustrating.

Daniel Lee

February 28, 2025 08:56

Update - according to logs, it could be down to a recent update from our cloud-based security/network software

Rona

February 28, 2025 20:24

Hi Daniel,

Welcome to Box Community!

To help address your issue, I created a new ticket and a member from Box Product Support will be in touch, please keep an eye out.

Thanks for posting!

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