When you get a message "The requested page does not exist" this can mean various things:

1) You're using URL rewriting and have clicked a category or member profile which uses illegal characters. Your category names need to avoid using characters which aren't legal in URLs. Profile rewriting is best kept to new directories where it can prevent bad characters from being used in usernames.

2)The URL you're looking at is for an item which has been deleted.

3) There's no id parameter in the url. Check the link you're following. Ask for help if needed.