Windows - Do anybody know a the reason??  

CON is a reserve word in DOS which mean a device name 'console'. One cannot use reserved words as folder name, you could try also PRN which is a device name for printer. Back in the DOS days to create a batch file we type in command prompt:

COPY CON AUT0EXEC.BAT

Then we type the commands needed we press [F6] I guest(rusty me) then hit enter. The file autoexec.bat will be created.

now every is using windows only but earlier days dos was the operating system used. windows intially was build on dos only. in thoes os codes a restriction was place to use folder name similar to command name and so why yoiu can not use con as folder name,.

Oh,I never use Windows XP, I like Linux. Now I'm using Mandriva One.

This is one of the bugs of the windows xp. as I know con is a system folder which cannot be accesed by the user. when you create a folder with the name 'con' it assumes it as system folder and denies the access to you.

hehe, this is really nice trick ... i did not know about this ... i think i will mess my friend with this :)

Like every other thing windows also have some reserved words which can be use only for some special purpose.
CON is one of the reserve words in DOS and Windows which mean a device name 'console'. so you cannot use reserved words as folder name, there are many more words too which we cant use as a folder name or for other purpose, they can be used only to call windows in built functions.

CON is the extention of CONSOLE i think just like SYSTEM<

The reason is that Windows XP terms these names as "SYSTEM" folder names. In other words, these names are reserved only for the OS, that is, Windows XP, in this case. In fact, there are others that can't be created "directly" using Windows Explorer or Command Prompt, like CON, PRN, AUX, NUL, COM0, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT0, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, & LPT9.

However, there's a trick to create such folders. For example, if you wanna create a folder named con, just invoke cmd(Command Prompt) and type in the following:

md \\.\\c:\con

This will create the folder. But you won't be able to delete it through Windows Explorer directly(you'll get an error), so, if you wanna delete it, then type in the following:

rd \\.\\c:\con

This will delete the folder. Hope this helps.