I run 64-bit Windows 7 at work so, when installing the Sun Java Runtime Environment (JRE) in order to access some of my corporate applications, naturally I installed a 64-bit version of the JRE.

Application 1 ran OK, but application 2 (which is a usability nightmare at the best of times) refused to load.  Then, Dave Saxon was trying to access the same application (also from 64-bit Windows 7) and he realised what I had totally missed: I may be running 64-bit Windows but the default instance of Internet Explorer is 32-bit.  Sure enough, I ran a 64-bit version of Internet Explorer, accessed the application and it worked.

I haven’t tested if a 32-bit JRE installation would work with a 32-bit instance of Internet Explorer on 64-bit Windows but the key lesson here is to run up the appropriate browser architecture for the installed JRE version.