Safari Login Page Launches when connecting to wireless network

Hi,

This is a really strange problem, or it seems it to me, and I'm not that familiar with Macs, even though I have one, so will explain it as best as I can.

When I connect to a wireless network, whether this is because the wireless has been out of range, switched off, or when my mac book wakes, Safarai launches a window trying to connect to http://vodafonemobile.wifi, with a popup login box stating "To view this page, you must log in to area “level_15_access” on vodafonemobile.wifi:80." Below is a screenshot.

If I cancel, sometimes it comes back, but either way, i'm still able to connect to the internet or browse the network etc, so it doesn't seem to effect performance, it's just really irritating.

I've tried resetting Safari, clearing the dns cache and changing proxy settings, I've also tried running console whilst I turn off and on the wireless, but there's nothing obvious it could be.

I need to add that I don't have anything vodafone on any of the networks I use, so I don't think it's that.

Your help would be really appreciated, if you need more info, let me know.

Thanks

Richard