I hadn't checked my site account for a while until today and discovered that it had been marked as not validating back in January. I was puzzled because I hadn't been making any changes during that time, and only added one page in the previous month. I visited the 'Edit Account Settings' page, didn't change anything, and then came back to the advertisement details page, and found that the site had now validated. As I've not being paying attention for a while, is there any reason why this might have happened?
Yes, that's the strange thing - I tried it first and it didn't work, then when I went to the settings page and back, it had worked. One possibility I thought of is that my browser might be playing tricks on me - returning the same page instead of the updated page when I pressed the validate option. I guess if other people haven't had problems it must be just a once-off. I still don't know what caused the site to fail back in January though.