Just got the same error for the first time today and had to reboot (killall hildon-home didn't help). The phone was at 5 days uptime but I've made it to 10 before with no problems.

I'm running dual swap files so swap space couldn't be an issue. I had about 90MB free RAM at the time and 73MB free rootfs. Tons of free space on the eMMC and MicroSD. I have a few apps from -devel and -testing. For widgets I'm running Personal IP address, DCEW, OMWeather, Media, Calendar and RSS.

Too bad the error message is so vague.