Yesterday I reinstalled my OS (XP SP3) completely. I installed K-Lite Codec Pack 8.4.0 Mega and then I installed 8.4.6. I noticed that CodecTweakTool.exe isn't working well (I use it every time to disable "Mpeg 2 decoder DScaler5"). I uninstalled completely, installed 8.4.0, used CodecTweakTool.exe to disable "Mpeg 2 decoder DScaler5", installed 8.4.6, and this solved my problem.