Text Edit does not allow to store the file?

I have a mac system. I am using its "Text Edit" software. I have open a blank untitled document. Now when I save this in a particular folder with name "InitialScope", it does not allow me? Why? When i save this file with other name like 123, it was saved. I have check the folder it does not contain any other document with name "InitialScope". Then why it is happening? I have also tried saving the untitled document after writing some text in it but no success in saving it with same title?