I got that message on my Fascinate this evening followed up by "Memory Low". Based on the notice description and suggested steps, I deleted my message threads and emails and rebooted. No luck. I hit the icon in the notification area and it took me to Manage Applications in Settings. The first thing I noticed was how large the Samsung Media Hub had gotten. Having never downloaded anything from the Media Hub, I couldn't believe it was over 50 MB. I hit the Force stop button and then the Clear data button and voila - The error message disappeared.
Anyone else have this issue?