Hidden Pages

I have set up a hidden page on my site which is a Thank-you for purchasing page that links to Clickbank.

As a customer goes through the checkout of Clickbank the last step is redirected to this Thank-you page. Sometimes this ‘thank-you page’ works fine and other times it comes up with a ‘404 page’. Any ideas why?

Also on my site the link buttons to pages move around on the template. Some viewers see the buttons running into the writing on my home page and other customers see the template with no issues. Is this a glitch in their computers or the template?

Any ideas appreciated! Thank-you!