Can't open an excel fille that has been tied to my old company's Microsoft 365

Hello Danny W

Thank you for reporting this.

Losing access to your own file because of a job you have already left is genuinely frustrating, especially when the contents have nothing to do with that employer.

The message points to information protection applied by your former company. This is normally a sensitivity label or Information Rights Management. The protection travels inside the file itself, so it applies wherever the file is stored, including a personal computer or a USB drive. This is why a file that is otherwise entirely personal can still be locked. It often happens when the file was created, edited, or saved while signed in on a company device or with a company account, because a label can be applied automatically.

Before anything else, please make a backup copy of the file so that nothing is lost while you try these steps:

• Open Excel, go to File, then Info, then Protect Workbook, then Restrict Permission by People, then Manage Credentials, and check whether your old work account is listed. If you still have working credentials for it, sign in there and try the file again.
• Make sure Office is fully updated, then try opening the file once in Office for the web. Some protection policies need a newer build, and an out-of-date version can be the only reason access fails.
• Reply here with the exact wording of the message, including any organization name or error code it shows. That text identifies which type of protection applies and whether anything further can be done locally.

If your old work account is closed, the practical route is to contact the IT administrator at your former company and ask them to remove the label or grant your personal address access. Only that organization holds the keys.

Please note that this is a user to user support forum. Moderators and contributors, including external Microsoft employees, are not allowed to directly interfere with Microsoft product features or access back end systems.

Our role is limited solely to providing technical guidance on reported incidents, requests, or ideas. Removing this protection is not something a forum contributor can do.

I hope this helps. Please feel free to reply if you need further assistance.