A bottle neck in your hard drive(s) chain..or over heating.
Exactly what do you mean by "a bottle neck in your hard drives chain".
I edit AVCHD with the computer described in http://forums.adobe.com/thread/652694 and have no problems
My 3 hard drives for video editing are configured as...
1 - 320Gig Boot for Win7 64bit Pro and ALL program installs
2 - 320Gig data for Win7 paging swap file and video project files
When I create a project on #2 drive, the various work files follow,
so my boot drive is not used for the media cache folders and files
3 - 1Terabyte data for all video files... input source & output export files
How many hard drives do you have, and where is everything located?