VSphere Client and Invocation Exceptions

1I've spent the last couple of months trying to avoid reinstalling Windows, to repair an issue I was having with VSphere Client for ESXi 5 - whenever I clicked on a VM host, I'd see a message telling me:

An unhandled exception was raised as the result of a client invocation.

If you get this, or similar - check your hosts file (%WINDIR%\system32\drivers\etc\hosts) and make sure that if you've got any custom entries in there, the first entry is

127.0.0.1 localhost