Strange problem when playing multi-part rars

[grr]

Hi guys,
This is my first post, cheers to anyone who can help me out. I've been a long time user of VLC and its a really great app but I've recently had a strange problem when playing multi-part .rar files. When I open the rar (not r00) I can watch around the first half hour of a video file but then it cuts out like i'm missing the final rars. I've had this problem with several popular video files and no one else reports a problem. Its only started happening recently but its happening all the time. My first thought was that my downloads are being corrupted, but I've done an sfv check of the files and they're all OK. Wierd thing is that I can extract the files and they play completely fine. I've noticed that the videos cut out at around half an hour for ~50 minute videos. My second thought was that i might have faulty RAM... i still have to check this one out. This problem is not specific to VLC as its also happening with XBMC but I'm guessing they use similar methods to play rar files. Thanks in advance to anyone who can help me work it out.
Carl

So far I've only had this problem with mkv files,
just ruled out any hardware problems because the exact same thing happens on my wife's laptop and we're both using VLC version 1.1.11

[Jean-Baptiste Kempf]

what is the size of the mkv file?

[grr]

cheers for the response, its happened with a 1.4gb video at 39mins, a 1.8 gb video at 33mins, and a 1.96gb video at 32 mins.
Funny how it is cutting out around the same time depending on file size. They're all 720p videos

[grr]

Anyone have any suggestions on this? Or could someone point me in the direction of somewhere that could help? It's pretty annoying