Claudio,

it seems that for some reason my previous answer went lost in cyberspace,
so I am replying again.

//Did you have "on update cascade" and "on delete cascade" at the same time
on that PK?

definitely yes

//Do you remember if you got an error message when trying to drop the
constraint and you
//had to commit or disconnect to retry?

I cannot remember that, sorry

//You are another victim of thread synchronization granularity and
//internal locks on system objects.

I would have preferred to be a victim of an overdose of wine and sex, but I
use to accept what God sends :)

//Just drop it directly with a delete statement.

following Martijn's advice, I already did that and happily ev works ok.

Thank you

Duilio