To fix this problem, do the following:
1. You need a clean and patched up version of RTW.
2. Download all the RS2 files, as shown in the release thread.
3. Now, install the RS2 mod to a new folder, created on the desktop. Mine is named Roma Surrectum 2.
4. When the mod has been completly installed, copy and paste the entire contents of the Roma Surrectum 2 map folder, located on your desktop, to your freshly installed RTW game. folder.
5. The new launcher that has been created on the desktop doesn't work. This is because it is a shortcut that the installer has directed towards the Roma Surrectum 2 folder located on your desktop, which isn't a game folder. To fix this, right-click the shortcut and change the Target and Start In lines so that both point to your correct RTW folder.
So in my case, "C:\Users\Al Simmons\Desktop\Roma Surrectum 2\Roma Surrectum II.exe"
becomes "D:\Activision\Rome - Total War\launcher\Roma Surrectum II.exe"
etc.
6. If you did everything correct, the launcher on the desktop works. If it doesn't delete it and create a new shortcut from the "Roma Surrectum II.exe" file located in Activision\Rome - Total War\launcher.