The problem is caused by the NextGen Gallery and its default settings with PicLens
The usually fantastic NextGEN Gallery plug-in can cause this issue. It shows in the status bar of the browser as waiting for lite.piclens.com
The simplest solution!
Disable PicLens by logging into the back end of the site then choosing “Gallery”, “Options” and unticking “Activate PicLens/CoolIris support”
You will now notice that website load speeds are faster as there is no external request to PicLens.