<SetForegroundWin> Error

http://i.cubeupload.com/yxAX2r.png

As you can see, this error only occurs sporadically, and there is no pattern as far as which window it happens to.

All instances run on one PC.

This only started happening a few days ago; I've been using HKN for a few months. No changes in hardware or software in that time.

Resource usage: 28% CPU, 45% memory, + / - 5% variability on each.

Also, there seems to be about 100 to 150 ms of lag when successfully switching windows; this also started at the same time as I started getting these failures. Before this, switching was instant (or near enough to be human-undetectable).

Windows 8