Problem loading m4a alac files onto ipod

I've been listening to lossless files on my ipods for years. m4a/alac files. Now for some reason they won't upload from my hard drive to the ipod via itunes. Did apple change what file types are allowed to be uploaded? Ipod and itunes are all updated to most recent version of software. Any help would be appreciated. If I can't fix this I will have to abandon my ipods and find a player which accepts my files rather than convert all my music. Frustrating! Please help