PL/SQL :: ORA-20001 / Unhandled Error Occurred

I've a procedure and a trigger. The problem is when I call the proc from inside the trigger I get an error message saying that

Error: ORA-00604: error occurred at recursive SQL level 1
ORA-20001: Unhandled error occured!
ORA-06512: at "ITEX.REFRESH_XSD", line 23
ORA-06512: at line 21

Here're these two problematic parts:

PROCEDURE:
create or replace
PROCEDURE Refresh_XSD(TableName IN varchar2)
IS
-- Variable declarations.
XML_Schema xmltype;
BEGIN

[code]....

So we have an xsd for a table only once. However that XSD needs to be refreshed when the table is altered, or created when the table is created. That's the reason I'm trying to use that trigger. If I comment out the procedure call from the trigger, everything works correctly except it does not do what needs to be done.

As far as I know only can't execute DDL statements from system triggers. But there's not a single DDL statement in there.