I am currently playing a sorceress in act 1 normal and this message frequently appears while playing. I have played a paladin also and never received this message even once while playing. Nor have i had it come up at any time during act 2, which is where I'm currently at. It seems to randomly occur in act 1 for the sorceress only so far. While it does not cause the D2 client to actually crash, it does become annoying since it will freeze the d2 screen until "OK" is clicked twice.
Act 1 normal>Sorceress>HU Solo version