Dave One wonders quite what you are doing to get to that command line. This machine is running Windows 8.1 and has Therion 5.3.16 installed. On installation, Therion placed a shortcut in my Start menu. That points, as does Rowena's at "C:\Program Files (x86)\Therion\bin\wish86t.exe" "C:\Program Files (x86)\Therion\xtherion.tcl" Now, if I navigate to therion.exe at C:\Program Files (x86)\Therion\therion.exe I, too get a command line box and the message: C:\Program Files (x86)\Therion\therion.exe: error -- source files not specified. What I don't quite understand is why your machine doesn't have the correct shortcut installed. Graham