[ns] about the error : "Checking for XFree86-base... NO!" when installing ns2.27

[ma-haiyuan]

Hi to all!
 
sorry to bother you !
 
When I install ns-2.27(allinone),there is  a error like this:

Checking for perl... ok
Checking for w32api... ok
Checking for XFree86-base... NO!
Package XFree86-base is not present on your system.
Please install it using Cygwin's setup.exe
before trying to install the ns-2 distribution.
The above test indicates that your installation of Cygwin
is probably NOT SUITABLE for installing ns-2 allinone.
(More details can be found in the specific error message above.)
Do you wish to proceed regardless? [y/N] 
 
But when I was installing cygwin, i chose all the components.
 
Please give me some advices 
Thanks and best regardes!