I know of two cases on A300s where the Air Cond. Packs weren't turned on after take off and the A/C was through FL200 before the crew realised they weren't pressurising.
One returned to point of departure. Red faces after landing.
The other descended to FL80 to sort the problem and then continued to destination.
On neither A/C did the cabin go above 8000ft.
In each case all they had to do was turn on the packs.
For the crews sake, I hope this was a system failure, and not finger trouble.
Happy flying.