Rails 3.0 and counter_cache error

[casper_the_ghost]

Hello,
I’m working on a rails 3.0 project and today I tried to add a counter
cache column, but I keep getting this error:

ArgumentError: Unknown key(s): counter_cache

This happens with any combinations of rails 3.0 beta4, rc, ruby 1.8.7
and 1.9.2.

Regards
Andrea