Your Pet there seems to be a problem with the yourpetforums.co.uk link to the forum. lotsofcats & myself can't login (which is why I'm posting this as a guest. Hopefully this may also be seen by any other forum members to help them be aware of the issue.
I've raised a report with proboards who don't seem to be having problems & a response was made that suggests that the issue might be with the domain name& suggested trying the old yourpet.boards.net url
That works to access the forum/boards/threads/posts but login fails as reverts to yourpetforums.co.uk.
I'm going to send an email through the technical contact on the Yourcat website.