half my menu links work, other half don't

Hi

I am trying to build a site and have posted it at the following address

www.morpheusproductions.net

It is the services section menu that does not seem to work properly.

the first five links work and open up the text about that section, but when I try on the sixth link it goes to the index page. I cannot see why it is doing this as the code seems to be the same as the sections above.

I have run a w3 validator and the only errors are for the images not have alt tags, which I am currently updating now, but know that this would not affect this problem.

any advice and help is greatly appreciated as I really need to have this section working.

thank you in advance