Hi Everyone.

Was a little unsure as to where to post this so I said here.

Firstly I'm running Ubuntu Hardy Heron on an XPS M1530 laptop behind a HTTP proxy.
I've had it running perfectly for the last year with everything I want working fine behind that proxy.
As of late I've had an unusual problem with the update manager. Each time I try to check for updates with it, it fails to connect through the proxy, and subsequently can find no repositories.
What's annoying is that after this failed attempt nothing else be it Firefox, Pidgin etc. is able to connect to the net, while before they all work fine (I'm in Ubuntu as I type this). The only way to rectify this is a reboot. The same thing also happens when running sudo apt-get update from the terminal, or when using Synaptic.

Does anyone have any ideas as to how to throw light on this? I'd rather not have to re-install it again.

It sounds like something is changing your proxy setting some time after you've been using the computer for a while. I don't have a Gnome based Ubuntu running right now so I can't test my idea. Try to get into the computer configuration section and check to see if your proxy setting is correct. Then check the proxy setting for Firefox to see if it is the same and if it is correct. Then check the settings for your other network applications for the same thing.