all links appear working but showing 500 internal errors to crawlers, ping etc HELP!!

When I use a crawler simulator the results come up with item numbers 8-22 as valid crawled links in amongst other non-product links. However I have 20 active products.

When using link checker software/sites when I type in the home page http://alphonic.co.uk it comes up with all product links as 404 errors,

However in the same link checkers if I type any product url in directly it gives a "200-OK" tick for the specific product link I have entered but gives all other products as 404 errors.

It seems as if direct entry to the links is fine but there is something wrong with the linking within the site?

I have done a lot of googling but came up with nothing at all that I can grasp at. The format of product urls is currently http://alphonic.co.uk/index.php?main_page=product_info&cPath=9&products_id=16

Is it going through some form of redirect that is casuing spiders to miss some/see them as dead?

If anyone could shed some light on this 404 url problem: see here for specific result http://www.2bone.com/links/cgi-bin/2check.cgi?spider_url=http:%2F%2Falphonic.co.uk&start=11&o=f

Thanks I really really appreciate the kindness and time of the community!

If you try a different validator, do you get different results? Try http://validator.w3.org/checklink

Working fine on that validator.

Many thanks to everyone who has put in the time to help me, I really appreciate it!

Hope this thread might help other in future too.

Pete.