Azure based Umbraco site - when logging in, I get logged back out immediately

Question

I have recently installed a website project on Azure and that was relatively easy to do thanks to great docs online. We are having a problem with the back office (admin) login though, it's a bit strange, as it didn't happen straight away, I shall elaborate....

When I go to http://www.keelycattschoolofdance.co.uk/umbraco/ it takes me to the login page, which seems fine.

(The url at this point becomes www.keelycattschoolofdance.co.uk/.../login.aspx)

I then login, which works and it starts to display the admin panels but then bounces back to the login and the URL becomes www.keelycattschoolofdance.co.uk/.../login.aspx

I am running this on Azure using the Accelerator, latest version of Umbraco and using SQL CE 4.0 rather than SQL Server.

has anyone seen this before?

Please let me know if you need more information, I shall respond :-)

Thanks in advance

Nick