Might be a problem with the Sky Broadband Shield which can decide to block access to particular sites as and when it feels like it, but doesn't always show its Access Blocked page (this may be affected by your browser as well). Try (1) a different browser (2) either switching the shield off completely (at your own risk - I've no idea if that's a sensible thing to do) or (3) configuring the shield to recognise imcdb as a legitimate site.