I apologize, I must have misread that particular sentence. If it just freezes then my guess would be a high level video driver. Memory, CPU, and power issues usually give a proper error.
Regardless, still try disabling MPE by going to Project > Project settings > General under the "Video rendering and Playback" tab, set Mercury playback to software mode if it's in hardware mode.
Alternately, try disabling any antivirus or automatic disk defragmenting programs (Perfect Disk, Diskeeper) if installed. These types of programs dig deep system-wise and can sometimes be the source of freezes as well.
Angelo Lorenzo
Fallen Empire Digital Production Services - Los Angeles
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