With the new forum software all links are automatically in bold, so there is no need to use bold tags [b] around the address.
IE, there is no need to include the b and /b in square brackets, like this example here:
Code:[url=http://www.google.co.uk/][b]click here[/b][/url]
So enter the following:
Code:[url=http://www.google.co.uk/]click here[/url]