It's working now - I only had the problem from my bluetooth>treo 650 Dialup networking connection, not from hy home network or office.

I saw this elsewhere:

Could be a couple of things... Some Anti-Virus, Firewalls, or Internet Security Suites block the referrer value and should be disabled on the users machine. You can disable this security check in the control panel, however it isn't recommended. You should also be sure all posible urls that users can login or post from are in the tracking box in the control panel (including the www and non www versions of any domains that you use).