Error using calendar

Hi all

I'm using a calender. But each time I use it in runtime it gives me the following error: "frm-40735: when-mouse-doubleclick trigger raised unhandled exception ORA-06508".

Strange thing is: it only happens the first time after the calendar is called! If i try a second time it works fine.

I use the calendar of STNDRD20.OLB and CALENDER.PLL. These are attached fine and procedures are compiled. Anyone who knows what could be wrong?

Thx
Stijn