It is in fact perfectly true that you cannot create a folder named "CON", nor can you rename an existing folder to "CON". However, there is no mystery surrounding this restriction whatsoever. The "team" at Microsoft, and a great many others besides, know perfectly well why you cannot name a folder "CON". "CON" and a number of other character strings are in fact reserved names that go back to the days of DOS and cannot be used to name folders or files.
Refer the below article from microsoft site
Microsoft MS-DOS reserves certain names for system device drivers. If you try to name a file using one of these names, you will receive the following error message:
Write Fault Error Writing Device
Abort, Retry, Ignore, Fail?
The solution is to change the file name.
Below is a list of default device driver names.
CON Keyboard and display
PRN System list device, usually a parallel port
AUX Auxiliary device, usually a serial port
CLOCK$ System real-time clock
NUL Bit-bucket device
A:-Z: Drive letters
COM1 First serial communications port
LPT1 First parallel printer port
LPT2 Second parallel printer port
LPT3 Third parallel printer port
COM2 Second serial communications port
COM3 Third serial communications port
COM4 Fourth serial communications port
To identify system device driver names, use one of the following two commands:
mem /d | more
debug d 0070:0000