This may be the popup blocker stopping the site, you can create an exclusion rule by launching Ad-Watch.

• Select the rule editor button on the left hand side.
• Tick use custom ruleset button at the top of the window
• Select ’New Rule’
• Create a name for the rule
• Select or value matches...
• Enter the word you want to allow as an example for http://www.pistonheads.com/ add the word pistonheads
• Tick the partial match box
• Select the Add rule button
• Finally to enable you rule to be used