No, not a problem with your builder!

Sometimes, as in my previous post, I may suggest that you create a file or rename an existing file with a new extension.

file extension In DOS and some other operating systems, one or several letters at the end of a filename. Filename extensions usually follow a period (dot) and indicate the type of information stored in the file. For example, in the filename EDIT.DOC, the extension is DOC, which indicates that the file is a word processor file.
www.west.asu.edu/achristie/545/webgloss.htm

If you’re a Windows user, this could pose a difficulty for you if you have all the default settings, as many file extensions are hidden from you.

To make sure that you can see a file’s extension, follow these steps (Windows XP):

  1. Click Start and open My Computer
  2. Select Tools > Folder Options…
  3. Click on the View tab
  4. In Advanced settings: make sure that the option “Hide extensions for known file types” is deselected (no tick in the box)
  5. Click OK

Now you will see file extensions for all of your files.