Parallels crashing

Parallels has started crashing. I have installed it numerous times with different updates since october 2007 on my macbook pro (details below). Each time it seems to run well for a month or so and then it usually states that it can no longer find windows (I am running in bootcamp mode and windows is definitely there) and stops booting up as a consequence. Usually when I delete the virtual machine and create a new one it works again. This time the virtual machine boots up ok but then crashes after 30 seconds or so with no explanation. Any suggestions? Considering this is a generally very good piece of software I am disappointed about how unstable it is.

Suggestions appreciated

Thanks

Model Name: MacBook Pro
Model Identifier: MacBookPro3,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.4 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache (per processor): 4 MB
Memory: 2 GB
Bus Speed: 800 MHz
Boot ROM Version: MBP31.0070.B02
SMC Version: 1.16f8
Serial Number: W87370MMX92
Sudden Motion Sensor:
State: Enabled
Osx 10.4.11