cannot set terminal X11

[David V. <va...@am...>]

I installed gnuplot Version 4.2 patchlevel rc2 and everything works  
fine except that I cannot set terminal to X11.  When I start gnuplot  
the following appears "Terminal type set to 'unknown' " and set  
terminal command does not show x11 as an option.  I can plot to  
postscript files etc..but not to screen.
David