You will probably need the full path to the script file. If that still doesn't work, try the following:
C:\Windows\System32\FTP.exe -v -i <C:\insert_path_here\ftpscript.txt
The redirection symbol "<" tells the command processor to get the console input from the named file instead of the console.
You also shouldn't need the path to the FTP program, or its suffix. You should be able to just use the command: FTP. Windows will, by default, add the .exe to the command and should automatically search the path you've specified.