[bojan]

Well, just now I had a chat with Canon Service in Sydney (where my camera is at the moment).

During that conversation (they were very polite and they appreciated everythig I told them), couple of interesting things surfaced...

- First, they are sure it was shutter because the camera has internal, and much more specific logging of events.. and that log clearly indicated that every time error popped up the shutter was to blame (I wonder now why this specific log was not displayed on the screen, instead of that notorious and non-specific "error 99" ?)
- Canon does not specify the life of the shutter, because this will depend on many varables.
- The technician who was taking care of my camera was himself puzzled by its behaviour (4 shots, 5th with error). So he decided to replace the shutter just to prove that the shutter was failing. Apparently, the problem was fixed with this replacement (but why error 99 came up after every 4 shots still remains the mystery..).

Now here follows the most interesting part:
- They told me if I do not accept their quote ($420), they will undo the fix and I can have my camera back as it was, no charge.
- I said "what a waste of an effort.." and then they offered me to send me camera back in the current state (that means repaired) if I agree to pay them the original limited sum that I agreed upon when leaving the camera in their office in Clayton (it was $250)

Well, I agreed to this, an so this saga will soon be over.
And they will give me 6 months warranty on shutter and labour.

However one issue is still unresolved: What if it was the software error.. or some intermittent problem with circuitry, which was (possibly temporarily) fixed by connecting - disconnecting cables and whacking the hardware in general? This would have been possible to put to test by installing back the old shutter.. in which case I could have ended with 250 in my pocket?
But I decided at this point in time not to be too difficult to them.. And I will have warranty so next 6 months I be shooting images like crazy :-)
Happy ending.. I hope :-)