Did you maybe paste some step notes (title/description) from a web browser?
If yes, there is a known issue that could cause it to fail if these contain unsupported tags.
If the above is true, please try exporting an empty project to verify that it works. If it does, you might have to paste the content of title/description via Notepad, so that all extra hidden tags are removed.
Additionally, if you could send us the ‘broken’ step that causes the file to not export properly (the .ssp file of just that step), we could make a permanent fix