Randomically pages of my website show a strange xml code page

Hi guys

This is the message I am getting when I am in a on my website and click on a link to open:

This XML file does not appear to have any style information associated with it. The document tree is shown below.

and then a xml file is showed

It happens randomically and after a refresh the web page shows the right content.

Any ideas ?

thanks in advance
Ciao

The page I need help with: [log in to see the link]