iMac won't boot on mondays –- only in "safe mode"

Last monday and today again I am coping with the same problem; my iMac won't boot by itself. After turning it on, it will go to the grey screen, give me the wheel and then I'll only see the "no go"-sign.

Last monday I deinstalled LittleSnitch and from then on I could boot again normally. But today, without LittleSnitch, I can only boot by entering "safe mode" (pressing "shift"-key during boot time).

I have done all the usual things: clearing NVRAM, checking access rights -- no change. The harddisk is fine; no errors. When I boot from an external drive with X.5 everything's fine and I can access all files on the internal disk.

When booting "verbose" I can see messages that hint at com.apple.driver.AppleFileSystemDriver and kext.com.apple.iokit.IOStorageFamily not being loaded or found.

What are these files there for and how can I replace them with working copies without reinstalling the entire SL system?

Usually, I turn off my Mac only on fridays for the weekend. From monday to friday I just send it to sleep. I initiated a couple of reboots during last week that worked just fine. I don't remember having installed any updates or system-level tools that might cause interferences.

Any help appreciated ...


Jason