This is a problem I've had for pretty long in windows 7. Basically what happens is after a few runs, the keyboard starts beeping when you try to move. After I did a search, it appears that I'm actually not alone.
http://vindictus.nexon.net/Community/#%2Fshowthread.php%3F279576-Keyboard-beeping-lagging
http://archive.klyptotech.com/VindictusTechnicalSupport/6681569-Keyboard_Spasm_Issue/1
http://archive.klyptotech.com/VindictusTechnicalSupport/6461677-Keyboard_beeping_and_lagging/1
All these people have the SAME issue that I used to have and noone ever had a solution.
I have a solution to it (kind of), except it's not really good. Personally for me I never get that issue on windows vista or windows XP, so I think a OS switch might be the only fix in this case. It's not a perfect fix, but a fix is better than none at all, I guess.
Let me know if you have a fix that doesn't involve a different OS.
Edit: Move it to Vindictus discussion I think. I posted it in the wrong section by mistake.