Errors when trying to filter pages

I am have a strange intermittent problem. When I try and skip through pages I get an error message

I have attached a screenshot.

What on earth could this be?

Screen Shot 2013-05-22 at 09.10.12.png

Hello AfricanHacker!

Have you tried to clear your browser and cart cache. To clear cart cache, please add &cc to your admin url and press enter.

Best regards, Alt-team