worldly wisdom 
It is about to become my motto:
Whenever you look for a program bug, whenever you search the source of a strange symptom, whenever you almost despair
Remind yourself
in most cases, it is the simplest, obvious solution.
- if your car does not run, check the fuel
- if the network is down, check the wiring
- if you are sure, this cannot do that, check who else is doing it
Todays experience told me this once more. At least, our code is running fine :)