Spent about 20 minutes wondering why Plink (part of the free PuTTY SSH suite) was acting extremely oddly on my machine - not displaying help when run with no arguments, and completely ignoring PuTTY saved session configurations, and generally not working at all.
On the off-chance, I downloaded the snapshot release of Plink (from the same page) and it worked straight away. Argh! A completely useless buggy version has been the official release since 2007?!