GD Library 2 with FreeType support. Addenster i strongly believe the sign up issue is due to not having GD Library 2 with FreeType support installed. i had that problem and when my host install it, It all got solved.
Owen how can i sort this & Ibrahim no just when i added a subdomain it woulded work, then my host sorted it now my site want login, im still waiting for them to get back if they have sorted it :(