sansa clip plus and itunes - how to transfer files

Hi DrMike - thank you so much for your suggestion… but regrettably it didn’t work.  

I went to iTunes>Edit>Preferences, clicked the Import Settings tab, and changed the setting from AAC encoder to MP3 Encoder.   

I then highlighted an album’s worth of songs.   Right clicking didn’t bring up the option to convert, so went to the “Advanced” men and chose “Create MP3 version”, as you suggested.  

Under each original song there appeared a duplicate.   There was nothing on my iTunes interface (that I could see) to tell me either what the original file types were, or what the new file types were.   I just presumed that each new duplicate was an MP3 file.   

When there was a full series of duplicates showing on the screen  I copied them.  

I then opened up Windows Explorer…Sansa Clip +…Internal Memory…Music.   I right clicked to paste in the new files, but again, the option to paste was greyed out…

I am still not fully convinced that the files in my set up of iTunes are not MP3s.  Can it be that the person who guided me through setting iTunes on my computer up in the first instance organised that they would be registered as MP3s?   It seems odd that the first time I copied and pasted the files (an assortment of completely different tracks of jazz and classical music), that they all transferred fine - I guess there were about 4 or 5 in total, but they all played perfectly on the Sansa Clip+…   It was only when I tried again later that I had problems.  

Thanks for trying to help though, I really appreciate it.