I really don't know why all of a sudden people have trouble adding songs to iTunes. Maybe some update (I don't let mine connect and it works just fine)

Just a thought (not the best way) but you could try clearing your iTunes Library then copying the songs in the Shared folder just in case something goes wrong. Now use iTunes to convert to m4a or ACC and add all the songs from the copied folder and then try adding those to your iPod.

P.S. I have never tried this myself since I don't own one, but it's worth a shot