problem with transfering AVI-s

Problem I face is veryy odd. Network in my company ( tv station) worked just fine), but few days ago we face huge problem. While transfering AVI files we receive them on other side of network full of drop outs and with large mistakes. We have 100 Mb switch, which we chaange and everything is the same. also we change network adapters, and everything is the same, also. colud it be that mother board of computer which send files is wrong or……….
please I need urgent help or answer.