After an upgrade to 2.0 go to "Configuration" -> "Hosts" -> "Items" (of any host) and look down for the error:

ociexecute(): ORA-00932: inconsistent datatypes: expected - got NCLOB [include/db.inc.php:458]
SQL error [ORA-00932: inconsistent datatypes: expected - got NCLOB] in [SELECT DISTINCT i.*,f.triggerid FROM items i,functions f WHERE i.itemid BETWEEN 000000000000000 AND 099999999999999 AND 1=0 AND i.itemid=f.itemid]
ocifetchinto(): ORA-24374: define not done before fetch or execute and fetch [include/db.inc.php:606]

You can got to Oracle command-line (e. g. sqlplus) and execute next query in order to reproduce the error:

SELECT DISTINCT i.*,f.triggerid FROM items i,functions f WHERE i.itemid BETWEEN 000000000000000 AND 099999999999999 AND 1=0 AND i.itemid=f.itemid;

An error points to "i.*", selecting all the fields of an item. This is caused by the change of the "description" field in the "items" table from "nvarchar2(255)" to "NCLOB".