dateByAddingYears, Tiger & Leopard, and losing my mind

FROM : Michael LaMorte
DATE : Tue Jan 01 23:32:33 2008

New Year's greetings to all,

I'm a relative Cocoa n00b, (came over from AppleScript land) and would 
appreciate any help (or handholding) I can get with this problem. I've 
Googled, searched through my stack-o-books, hit #macdev on IRC, and am 
still stumped. Hopefully someone here can shed some light on my problem:

I have a relatively simple program that was working fine under Tiger, 
but for some reason broke under Leopard. I can take the compiled 
executable and copy it to a Tiger machine and it will work fine, but 
under Leo it hangs at a certain point. (Read on for clarification.)

It's a CoreData app with a simple schema, one of the data fields is a 
Date. When creating a new record, I programmatically set the date to 
the current date using the following:

      [self willAccessValueForKey: @"theDate"];
      [self setValue:[NSCalendarDate date] forKey: @"theDate"];
      [self didAccessValueForKey: @"theDate"];

Stepping through with breakpoints and NSLogging shows me that this 
works fine.

In the interface, I have the date displayed in an NSDatePicker with 
stepper. (Generated by option-dragging the CoreData model into the IB 
window and having IB generate the interface elements for me.) So long 
as the user doesn't change the date, they can input other data into 
other fields, create new records, etc. There's some custom logic 
executed on the theDate that also works fine, again so long as the 
user doesn't change the date with the interface.

The instant the user changes the date in the UI, and even if they 
change the date back to the current date, the application becomes 
unresponsive to input to any other field, and the debugger window 
shows this:

*** -[__NSCFDate 
dateByAddingYears:months:days:hours:minutes:seconds:]: unrecognized 
selector sent to instance 0x1ce630

Any bit of custom logic that uses the dateByAddingYears method invokes 
the error. At this point, the user can still change the date in the 
UI, but for all other fields, menu items, and interface elements, the 
app is unresponsive to user input, and the app must be terminated. 
Stepping through and NSLogging shows that the new date is reflected in 
CoreData properly, but any execution of dateByAddingYears, anywhere in 
the application, throws the same error.

Taking out setting the date programmatically, the same thing happens: 
setting (or changing) the date via the UI hangs the app.

All date variables are instances of NSCalendarDate, and I've checked 
umpteen times for stupid things like misspellings.

The odd thing is that none of this happens under Tiger, even after re-
compiling in XCode 3... the executable can still be copied to a Tiger 
system and run without error, but hangs up on any Leo system.

I'm at wit's end and have been trying to fix this problem on and off 
for 2 months.... Help!
- Mike

---
Michael A. LaMorte

          "In matters of style, swim with the current;
            In matters of principle, stand like a rock"
                          -Thomas Jefferson