Slow video play

When I install the latest K-Lite Codec Pack everything works perfect. But after a while (few days to 2 weeks) the video plays too slow, just like there are not enough frames per second. For example: I downloaded the movie 'Rocky', with the K-Lite Codec Pack 10.6.0.0 Full (17 July 2014) the movie didn't play smooth, especially when there was fighting involved. When I then downloaded K-Lite Codec Pack 10.6.5.0 Full (6 August 2014), the movie played smooth like it should. As video player I use Media Player Classic. So what can be the reason that the movie first plays smooth and after a while with the same video player, the same codec pack and the same movie suddenly doesn't play smooth? And how can this be fixed? Anybody else noticed this problem?

Some other program must be messing with the codecs or their settings. Have you used any other video related programs just before the problem happens?

If the problem happens again, then make a log and post it here. That will help me determine what might be the exact cause.
Codec Tweak Tool > Generate Log