This might not be news to everyone but this issue was a new one for me. I went to go create a site for a client around the state of Connecticut. I had created multiple other sites using the first 3 characters of the state name; ARI, WIS, etc. So I then went to go create a site with the URL of “con” ……

And then……

Server Error in ‘/ Application with a 404 cannot be found error! At first glance this makes no sense. Your site exists, you can see it in site contents:

I found out that this was due to a reserved words list. This list is not directly within SharePoint, but within the fundamental rules of naming files in Microsoft, regardless of file system. Here are the words that you cannot use as the name of a site, library or list.

CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, LPT9

If you have created one of these sites you can still delete them through Site Settings -> Content and Structure.

Select your sub site and click Delete.