my file keeps becoming 'read only'

I have some .xlsx files that become 'read-only', on their own. I go to the 'Cmd I' to get the file info pane and I unlock it and change all the privileges to 'read & write'. and then re-lock it.
Then when I come to use the file it says it is 'read only' again.
It is infuriating as I am the only one using the computer and I don't want to protect the files.
What am I doing wrong please? Can anyone advise?
Many thanks in advance
Paul
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Do you name the files using spaces, /'s, \'s... or any other "odd" characters? If so, try renaming them using only text and numbers.

Where are you saving the files to? Once you change permissions on a file they should remain the same unless you're saving them to a location that's read only. For example: saving your Excel files to a drive formatted to NTFS.

Thanks very much for the kind assistance. Actually Dogbreath had the answer - I had a forward slash in the file title. I just removed that and everything was back to normal.
I am so grateful!
Regards
Paul

I'm glad I could help....my pleasure.