This is weird.
Did you have that systematically when using the "sort" option? Because it should not be related to that.
Maybe you can try to clear your IMCDb cookies, as that error is often rather related to that. Possibly some ads stored too much crap (as IMCDb itself does not store much in the cookies). After which you'll have to log in again.
To do so, in Firefox you click on the shield on the left of the address bar -> Clear cookies and site data.
In other browsers I'm not sure how you can selectively clear cookies just for one site (don't do it for all) but there should also be a way.