duplicate .txt file opened. Why? How can I fix this?

[pguild]

I give a simple command like

Run("Notepad",filename)
Note that filename is a valid file with a ".txt" extension in the current directory.

Notepad runs but two copies of the file appear. Why? How do I fix this?
Before running that command I check to make sue that the filename does not exist
with:
If WinExist(filename) == @FALSE
   Run("Noteopad",filename)
Endif