Clicking Browser's Back Button Shows An Empty Page

On my website www.lahabitacionroja.com developed using Php I am experiencing the following problem:

When a user with MS Explorer 5.0 or older clicks the back button on the browser it shows an empty page...
If you try with MS Explorer 6.0 this problem doesn't happen.

Does anybody why it happens and if there is any easy solution??

Is it a browser issue, an Apache issue....