Could be related to configuration, but more likely to be your code.
I don't see that much date related stuff in this code. You say it happened after 1 Mar. That sounds like an artificial boundary to me.
As in somewhere you have configured in the system "valid dates" and that list now needs to be added to.
Thats a big JSP. A lot of it seems to be duplicate code, and fingers itch for refactoring...
Can you narrow down which area of code might be a problem? Does this error occur happen on various parameter values?
You are finding out first hand why it is recommended not to use scriptlets in JSP - they are a demon to debug.
This particular exception being logged (from the exception handler) is hiding the real cause of the problem.
What server is this you are using? Tomcat? iPlanet? What version?
What version of java?
If you can't get a stacktrace that shows the root error, then the next resort would be peppering the JSP with log statements so that you can track at which point it is blowing up on you.