Something that's been talked about within this thread several times, yet a picture is worth a thousand words. When using LAA, or another "4gb patch", you need to make sure the "Properties" within the "SH4.exe" file is
NOT set to
READ ONLY.
The SH4.exe file is in your main game folder.....usually defaulted to being named "Silent Hunter Wolves of the Pacific". Look for the black sub icon. There are two icons like it, but only one is the SH4.exe file:
As above, right click the "SH4.exe" file to show its "Properties" menu. Under the "General" tab make sure the "Attributes......Read-only" box is unchecked. If it is check marked, uncheck it as the above image shows; then strike the "Apply" key, saving your settings. I'm pretty sure the game has this "Attribute" set as default to "Read-Only" (the fix will not work as long as it's Read-Only).
This will set up the games .exe file to accept the changes LAA or any other 4gb patch will make when you add it to your game.