Forms :: Trigger Causing Error ORA-06502 And ORA-01403?

My layout is working well enough triggers though are causing me some problems. I am getting the following error message just about every time I write a trigger so I am getting the feeling I am doing something fundamentally wrong. Like there is something I am just not getting because I am getting this error on the simplest of actions.

The error:
FRM-40735: WHEN-VALIDATE-ITEM trigger raised unhandled exception ORA-06502.
--------------------------------------------------------------
ORA-01403: no data found

The trigger is this:
cs3_prog.set_date_mode;

this calls the following procedure in the package cs3_prog:

procedure set_date_mode IS
BEGIN
:cs3_data.street := 'something';
end;

this in the past did a lot more but I kept throwing stuff out to see what could have been causing the problem. This does actually work if I ok through the first error message and then try entering data again into the field the trigger is tied to. On this second firing of the trigger is does successfully alter the value.

Just the fact that this is happening every time I create a trigger and it seems to happen regardless of what I have the trigger doing leads me to believe I have something fundamentally wrong and I would love to have it set straight.