Tony asked me to take a look at this for you.
First thing I notice is that your site is loading the bootstrap javascript library twice (which can cause a lot of problems). I suspect this is caused by your menu module or gallery addon??
Your bad request message is triggered by a security addon on your site/server. when you try to check for conflicting events. this is the underlying message
400 - Ha estat detectada una seqüència que podria significar un atac hacker. Seva petició no pot ser processada.
You either need to find the security setting causing this and change it or stop checking for overlapping events in JEvents. I think its your 'Securitycheck' firewall addon that causes the problem