If you have a Steam game, you have to use the Steam way of starting. When you copy the folder and move it on your own, it does not take the Steam Licensing with it, and therefore will not start. With Steam, use their front-end to move it first, then run the game from there. After that, copy the game folder, and paste it into the same "base" folder. Then add the game to the Steam Start menu as a non-Steam game, and now it will properly check its licensing and run.
The way I make my copies in Steam, is I use 7-Zip installed in Windows, navigate into the moved Steam folder for my Silent Hunter Wolves of the Pacific folder, use <Ctrl><A> to "Select All", then a right-click with the mouse, and choose the "7_zip ---> Add to archive" context menu item, and create an archive inside of that folder. I then copy that archive, and then paste it into a folder I created in that "Games / Steam / SteamApps / Common" folder that I named. As an example, I made a folder and named it "FotRSU" for my Fall of the Rising Sun, and another named "TMO" for my Trigger Maru Overhauled, etc. Paste that 7zip archive into each of the folders, and then use "7-zip --->Extract here" to extract all of the Silent Hunter Wolves of the Pacific files into that folder. You can delete the archive after that, or <Ctrl><X> to cut it an move it to another folder. Now do the modding. Do MultiSH4 for a new Save folder name. Then activate your 4gig memory manager on the SH4.exe file (you ~have~ to do the 4 gig app last, else MultiSH4 fails). Open the Steam App on your computer and log-in. Use the "
Add non-Steam game..." instructions to add the new installs, one at a time, to your Steam Library menu. After adding them, change their names to reflect your mod install. Now, which ever way you use to start the game, it will go through Steam to do its licensing checks, and should run just fine, including after you have it modded. I would leave the original Steam Silent Hunter Wolves of the Pacific install(s) alone.
