"Could not get shell folder ID list" Java exception

I am developing a Java application on a Vista Home Premium system. Suddenly,
whenever I click on a browse button which creates a File Open Dialog
(JFileChooser), I get an exception "Could not get shell folder ID list". This
has always worked before and I have changed nothing that could cause this
problem. The program runs correctly using the same jar file on my laptop,
also running Vista Home Premium.

I am convinced this is a Vista-related problem. Another weird thing is that
when I start Windows Explorer, it starts up in C:\Windows\System32 which it
never did before. Could these two things be related? Could you please explain
what the original exception message means? (I have re-installed the Java
runtime environment to eliminate that as a problem). Thanks for any light
you can shed - I am at my wit's end here!