I have a problem with jQuery and PHP.

When I put the suffix of this web page as .php the date picker doesn't work but when the file extension is .html it works fine.

The page is this:   http://www.rateyourdigs.org.uk/add.html

It works fine as either .php or .html on my computer when previewed in Firefox,Safari,Chrome.

I'm really confused.  If anyone could help, thank-you!