"All of a sudden" does in fact mean that the links worked before. We've earned some commission with that site. They stopped working even though we hadn't changed anything to the site.
Just now I checked again and it seems the links are working again even though I haven't made a single change to the site or in the factory.
Do you know how we can prevent this from happening again? I'd be glad to pm you the credentials to the site if you think that might be useful to find the cause.
Thanks for your help.