This extremely irritating ad doesn't appear when using IE11, but is there at both top and bottom of the forum page when using Chrome, which I recently decided to use as my default browser.

Thought I'd summarise the things I've tried to get rid of this ad, which seems to originate from a website called aldaniti.net, which has an extremely poor rating to say the least:
Ran Malwarebytes (free) - nothing found
Ran Adwcleaner (free) - found several 'PUPS' which I deleted, although none of them seemed to relate to aldaniti.
Ran Hitmanpro (free trial) - found 3 tracking cookies which I deleted.
Nope!

Went into Chrome's settings>advanced>reset settings to disable browser extensions and delete all cookies.
Success!

This sort of stuff is way outside my comfort/knowledge zone so I can't guarantee it will work for anyone else, although the scanners mentioned all have good reputations and it's extremely unlikely you will suffer anything more than the inconvenience of having to manually log back into any site (including this one) which uses cookies to store your login details.