Forum Discussion
Unable to open Excel file
Re: File "Books ti read.xlsx" (sic) Error message: 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...
Since this is probably a template, I would first recommend changing the file to .xltx format (meaning the file extension) instead of .xlsx format.
If this does not help and the error only occurs with this file, I recommend following this link with the attached steps.
Hope I was able to help you with this info & link.
I know I don't know anything (Socrates)