Site is asking for webmail login username/pass ?

Hi.
I am new to WordPress, experienced with Joomla. I have transferred a WP site to my server for a customer and set up the DNS exactly the same as dozens of other sites i have.
the problem is that occasionally on the live site i am getting a webmail login box opening up asking for username and password.
I have never seen this randomly happen on one of my sites before and apparently it didnt happen on the old server, can anyone shed any light on why this might be happening please ?
many thanks

http://mygolftrip.co.uk