Time machine error

Hello,

I got an error on TM recently that said "Files can’t be copied onto the backup disk because it appears to be read-only."

I think it's because there' only 49GB left on my 1TB drive... But I do have the selection in TM to inform me when it deletes old backups. It doesn't seem to have ever done that though.

I also recently created another account on this computer, could that have had some effect on it?

I'd be happy to go whipe out two years worth of backups as well, just not sure what to do, but I do want to return it to automatic operation.

It seems normal after a restart, though, so do you recommend doing anything at all?