Sorry for the last post, i just solved the (false) issue by myself (as a big boy for once): in the "Incomplete" folder, there r 2 files for the movie that I downloaded, one "preview" (which has codec problem) and the other one is actually working fine.

The problem seems solved for the moment, however it still is not normal that Limewire made those 2 files instead of one and didnt automatically transfer the donwloaded file out of the "incomplete" folder... maybe is it a bug generated by "Preview" ? as i trie dto preview during the downloading...

Cheers!