If you see this error when trying to leave a comment on a website it is caused (at least in some cases) by the Growmap Anti Spambot Plugin:
The cache may have been out of date. Use this link to view a fresh version Essex Folk Music – Information, Gigs and Venues in Essex
Error Code: nc03
I was alerted to it by a commenter who tried and failed to comment. I have updated the rowmap Anti Spambot Plugin to Version 1.5.5 but the problem still happens. So it has been de-activated on all blogs where I run it.
No idea of a solution at the moment, other than to not use it.