Hello,
Thank you for your question.
I would like to suggest you to check below troubleshooting steps.
- Give Every one Permission and Select Replace Owner and Replace all child object from Advance option. Afterwards, perform decryption of files.
- Also , try to access this files from Windows 10 PC and Decrypt it.
Please have a look on below Microsoft thread which may help to resolve this issue.
https://answers.microsoft.com/en-us/windows/forum/all/error-0x80071771-the-specified-file-could-not-be/6ae895e2-f154-40de-b970-e93d3fc8f060
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