dwm + xterm


I have a problem with DWM.
I start Xterm with Mod1-Shift-Return. When I press these buttons sometime Xterm does not start.
I hear only a Beep, but there is no more Xterm window. In average I have to press Mod1-Shift-Return five times to open an Xterm terminal.
This is the same in wmii and in xmonad too, but in kde it works well. I have tried to find any solution on the Internet, but had no success.

All my ports are up to date.

Best wishes