Sounds like the wp_nonce_field() kicking in, suggests that it’s not seeing the correct referer to allow the form submission to proceed. I’m not that familiar with W3 Total Cache but perhaps – if it is – it shouldn’t be caching the sign up page ?
Thanks for the tips. I manage to solve the issue by disabling Page Cache and Database Cache in ‘W3 Total Cache’
We’re aware of issues with certain types of caching provided in W3TC and BuddyPress, but I’ve personally not tracked down which, where and why
I’m getting this problem all of the sudden, too. I think it just started with the last W3 update. If I disable W3 it is fine. Also, if I manually go in and empty all of the caches it works fine, too. But, if I leave it alone for a few hours I will again get the the “Are you sure you want to do this?” message. Empty caches again — fine again.
I will disable the page and DB caches and see if that will keep it working over the course of the day, but really, if I do that what use is W3? Is it even worth keeping active?
I might first try just making sure the register page isn’t caching. I added “/register/” to the “Never cache the following pages” section. Not sure if that’s the correct syntax or not, though. We’ll see …