Login Issue

When i got to the homepage, everything works fine! It logs me in, and i can use all of the following areas of the site and remain logged in :
Home, Road, Mountain Biking, Commuting, Beginners & Family!

But as soon as i click on the "Training and Events Tab/Section it logs me out, then when i log in, it redirects me to the forum, then when i go to training and events after logging in, I am logged out again etc etc...
Am i doing something wrong or is there a problem!