Unable to register new users

Hi there

I'm using joomla 2.5 (updated) and the Startup Template. I'm unable to register new users. the link for my website is http://www.bajaboo.com

When I try to register new users (in order to have some fake test users), i receive the message "Invalid Token".

I tried to install Jomsocial, in order not to use the joomla instalaltion process, but, in this case (using the jomsocial registration form), i cannot continue after the first step (name, username, mail and password).

I receive the "invalid token" message also when i try to log in with existing users.

I tried to remove cookies and every possible combination of the cache settings.

I cannot understand how a company like Gavick continues to receive negative feedbacks (this one is not the first) about registration process.

I hope you can help me quickly, thank you in advance.

ok, i found a partial solution to that problem: it's the Search Engine Friendly URLs

when they are set to Yes, I don't know why but they cause this problem; when I set them to No, and so I don't have SEF urls with all the following consequencies, it looks like working.

Is there a way to have SEF urls (that, apart from registration form, work normally) also for the registration process?

I don't want to have chaotic urls, since i paid for a premium product

Seriously?? no solutions??