Starting from Oracle 10g, Oracle have changed the error code 1401 to 12899. For applications migrating to Oracle 10g make sure that there is no direct reference to -1401 anywhere in code.
There can be either
PRAGMA EXCEPTION INIT(field_length_error, -1401);
if sqlcode = -1401 then
type of errors handled in the program.
Use the following query to (not fully) find out whether there are any references to the code or not.
select name,line from user_source where text like '%-1401%';
If there are any references, change them to -12899.