Not every time, just occasionally over last 2 days. I know you are having issues with posting on IE and multiple posts, so held off from flagging this up!
It says something like "The website MN says please enter message/subject field" and then I click the ok box and it goes away. It pops up as soon as I open a page. Of course now I want to see the exact words then it is not doing it in the other tab! Typical!
I can get a screen shot next time if you like?
Anyway not urgent as it all still works for me so am not complaining just flagging it up. 
- and yes I do mean gin not grin!