Control throws error when compiled in release mode. but works nicely when compiled in debug mode.

Question

This will sound weird but its happening Control throws error when compiled in release mode. but works nicely when compiled in debug mode. I have created class library which has several user controls, now one of the control is throwing null reference error.(object reference not set to instance of object). To trap exact place of error I recompiled this dll with debug option . to my surprise control works with out error when I compile with debug option. I tried switching .net frame work version 1.0 & 1.1 same thing happens with both. How I can trap error if I can not get error in debug mode? and what could be reason for this behavior