why computer system unable to create the folder named by CON?

Answer 1

CON is a DOS-level reserved word, like LPT, COM, and so on. You can't use that word.

Answer 2

Your computer sounds like a Democrat and wants nothing to do with CONs.

Actually, it is a reserved word. CON is short for console and it is used in DOS as a way to pipe data intended for the hard drive or a disk to the screen. There are other reserved words too like NUL, PRN, LPT, LPT1, LPT2, COM1, COM2, etc.