FIREWALLS can cause problems because they can block the cookies used to allow you to log in.
If you find you are logging in but cannot access menu items (for example you cannot open the MANAGE SITES page), or you think you are logging in but you are unable to navigate or the system bounces you back out again, then this is almost certainly caused because your Firewall (NORTON, MCAFEE etc ) has blocked a Cookie which helps you to log in.
To fix this, go to the settings in your PC Firewall and specifically list www.singlepropertysites.com as an approved website. This will allow the right cookies to be stored on your PC.