prototype not working with rails 2.2.2 ?

Hi,

i made an application using rails and prototype and all worked fine...
But today i upgraded rails to 2.2.2 and from that moment when i open
the webpage with firefox it gives me an error like "object is null"
and some prototype "helpers" doesn't work at all as for example the
observe_field...

Can anyone help me?

Thanks,
Riccardo