[SOLVED] good order for deallocating in ecpg

In a pgc code, I do a kind of:

exec sql begin work;
exec sql prepare my_rqt from :rqt_insert  ;   
exec sql execute my_rqt using :foo, :bar ;
if ( sqlca.sqlcode == 0 ){
    exec sql deallocate prepare my_rqt ;
    exec sql commit ;
} else {
    exec sql deallocate prepare my_rqt ;
    exec sql rollback ;
}

when insert works, everything is fine, but, in the othercase, I get an error on the 'deallocate' statement :

sqlca.sqlstate : 26000 : invalid statement "my_rqt" on line xx

If I do deallocate after rollback, I don't get this message. I can't find any sample code of this in any documentation.

Thanks for any help on the right order to do such things.