Hello,
I installed the Sailfish to my n9 and I followed that guide http://wiki.maemo.org/Sailfish. After that the apps of the MeeGo will crash suddenly and the phone might reboot also. For example I downloaded the apps from Nokia Store and Store app crashed several times. In addition N9 QTweak crashed all the time when I was trying to install Unrestricted MT-Toggles. When the phone starts the warning message appear on the screen. It looks like this: http://img577.imageshack.us/img577/8671/photoqp.jpg
Any ideas?

That warning screen is normal on an n9 that has been repartitioned and/or had its kernel replaced with a non-official version. It can be removed, but that must be done before you do the flashing. This process is detailed in many of the flashing guides, but I'm not sure if it's in the Sailfish instructions.

You'll also find your password caches in Harmattan aren't working properly after this. Could be the cause of the crashing. Or the repartitioning could mean you're short of storage space, or could have adversely affected the harmattan filesystem.

Anyway, the solution is to re-flash the n9 back to the standard partitions and kernel. The warning will go away, any filesystem problems will go away, and you can prepare properly for another sailfish install if you want to try it again.

See here: https://wiki.merproject.org/wiki/Nem...ur_N9_firmware

Your problems were caused by entering Open Mode without preparation.
What you should at least do, is to:
1.) disable open mode warning before entering Open Mode
2.) go to Open Mode by back-to-back flashing, so you will have no aegis conflicts
3.) install the applauncherd tweak which will prevent your applications from closing when you install new software.