Can´t free space anymore after upgrade from P8 to P9

Pleeeeeease, help! After upgrading from parallels 8 to 9 I cannot free space anymore. Thus, the virtual machine (with windows 8 installed) is growing and growing.

Problem: when I press the button to free space (configuration of the virtual machine), after a while the virtual machine tries to start and reboot windows again. But booting is not possible anymore. Booting screen says: No OS installed, please insert CD for installing OS..... something like that.

That means: freeing space leads every time to deletion of the system - in my case windows 8 was distroyed.

Was anybody else attacked by this embarrassing issue? I have no idea how to work around. Therefore, I deleted P9 and reinstalled P8. This cannot be the ending solution.

Thank you tons for help and your ideas.