SQL> ALTER TABLE GAZBX811.ARTICLES
2 DROP (DATEMODI);
ALTER TABLE GAZBX811.ARTICLES
*
ERREUR à la ligne 1 :
ORA-00406: param. COMPATIBLE doit être 8.1.0.0.0 ou plus


SQL>

Sorry but I have a french version. My client is Oracle 9.2

There is an Oracle system parameter called COMPATIBLE that is apparently set to a value lower than 8.1.0.0.0 on your database. This means that you can't do anything that was not valid prior to 8.1.0.0.0. The solution (assuming you are actually using a server of version 8.1.0.0.0 or higher) it to change the COMPATIBLE parameter to a higher value.

Where ?
in the orainit.ora ?

Yes, this is one for your DBA. Setting the parameter is described here.