The page you requested is invalid.

Providing the following information will help us troubleshoot your issue: 
The address (URL) of your Google Site:https://sites.google.com/site/bobblyobdob 
Browser / Operating System (e.g. Firefox 5 / Mac OSX): Chrome, Windows 7 
Copy and paste any error messages:The page you requested is invalid. 
Note: If you don’t want your site’s URL to appear in the forum, please use a URL shortener like http://goo.gl 

I have edit permissions for the above site and have added a number of other users (both with and without google accounts). To make the site viewable I have had to change it from Private to Can be viewed by anyone with the link. However, whenever any other named user tries to actually do anything on the site they are asked to sign in. As soon as they click the link they receive the error page - The page you requested is invalid. So they cannot sign in. 
If they log in to the google account and then select sites they are not shown the option to go the above - just create their own. 

How can I get the users to be able to access the site etc. 

Thanks