This happens when you have 2 or more procedures, with the same name, but with different numbers of input parameters.
For example, you have created 2 procedures:
CREATE PROCEDURE myProc(param1)
CREATE PROCEDURE myProc(param1, param2)
To delete the second one, you have 2 options:
The easy one:
DROP PROCEDURE myProc(param1, param2);
The hard one:
dbaccess DB -
select procname, procid, numargs from sysprocedures where procname like 'myProc';
UPDATE sysprocedures SET procname='myProcOLD' WHERE procid=2;
DROP PROCEDURE myProcOLD;
Even if the first method is dead simple, the first time I got called in the middle of the night for this same problem, I've chosen the second. My bad ...