Problems mounting and creating disk images after system upgrade

After upgrading my TiBook to Mac OS X 10.3.5 I suddenly couldn't open disk image files (.dmg extension). Couldn't find any solution on the net, but this line from /var/log/system.log gave me a hint:

Aug 13 07:50:51 localhost kextd[84]: a different version of dependency extension /System/Library/Extensions/IOStorageFamily.kext is already loaded

Something seemed to be wrong with a kernel extension. I vaguely remembered something about the kernel extensions being cached. How to update the kernel extensions cache is described here. Simply mark the extensions folder "dirty" by touching it (as root), touch /System/Library/Extensions, and the cache will be rebuilt.

This operation solved the problem for me.