Open the startup file for icewm (~/.icewm/startup)
find the line that reads "sleep 5"
increase the number to something like "sleep 8"
un-comment the line for nm-applet so it will start
log out and back in.
If you still get the little black square, increase the number a little more.
If the networking works okay then, you may ignore the warnings.. actually, you won't even see them.