NoSuchMethodError weirdness

Hey all,

I'm writing an application with some 3rd party widget libraries, which I
access as libraries in Netbeans.  Today I discovered that when I use
some of the components in my project, they throw NoSuchMethodErrors
which I took to be a fault with the widget library, so I started a new
project and tried to use the widgets, and they worked fine.  I added the
exact same libraries to both the primary project and the test project
and got the different results.  The stack trace indicates that none of
my code is causing the error, does anyone have any idea what could cause
this?

I've even imported the project's source into an entirely new project,
and I get the same result.  If I extract the code that uses the widgets
and place it in another project, it works fine.  I'm totally stumped.  
I've checked Netbeans' error log--nothing about this.  I'm using
Netbeans 6.0.1 (although the problem manifested itself on Netbeans 6.0).

Thanks,

Joe