I've ended up having to go down this path as I have a client who asked for an AECOsim build added to what they already have running. Only issue is I need to have SS2 and Structural Modeller running as well on existing projects.Ran this through my head for a while and to be honest..... I cheated a bit :-)Bentley, in their infinite wisdom, have kept the version numbers the same between SS2 and SS3 so getting the single appl.cfg file to work was going to be hard. The cheat I've used is to have a custom appl.cfg file for the SS3 build which sets the 811 version to my SS3 build:%if defined (_VERSION_8_11)MS_VER = MS811_SS3%endifI can do this with a small edit in the code for starting either SS3 MicroStation or AECOsim:'------------------------------------------------------------------------------------------' Start AECOsim_ss3'------------------------------------------------------------------------------------------ Sub startaecoss3If (oEnv("Phase")) <> "Legacy" Then objFSO.CopyFile SitePath + "MS811_SS3\Standards\data\std_appl.cfg" , AECOsim_ss3 & "AECOsimBuildingDesigner\config\appl\", OverwriteExistingEnd IfIf (oEnv("Phase")) <> "" Then WshShell.run chr(34) & (AECOsim_ss3) & "AECOsimBuildingDesigner\AECOsimBuildingDesigner.exe" & chr(34) Elsemsgbox "Please Select a Phase first !"End IfEnd SubOnce in a while you just have to cheat a bit :-)More soon.