That really could be anything; we need far more information. While it wouldn't cause that error, you don't seem to have anything checked, so even if you did export, it wouldn't output your translation properly. You're also using an EXTREMELY old version of T++, so I'd strongly recommend updating to the latest (free) version. That potentially may fix things, especially since older versions of T++ seem to throw that error way more commonly than newer versions.
In my experience, the "file not found" error is often caused by deleting or moving the "temp" file that T++ stores the data in, or the "cache" file from your T++ folder. If you've moved the T++ folder or your appdata folder, it can cause that problem due to T++ not being able to find that directory. If that's the case, you'll need to import your translation over to a new project, though since your T++ version is so old, I don't know if it has that functionality. Might need to copy line-by-line (or a "select all" "copy/paste" for each map) to a project from a newer version.