I have made a short video of the installing process. It seems that it works on some systems and not on others..
Maybe a thing to check; The installer assumes that the BR189 Folder is here: ..railworks\Assets\RSC\BR189Pack01\RailVehicles\Electric if it is somewhere else the batch file cannot find the files to copy. When unpacking the .ap file using 'extract here' this should be the case. If using extract to [somefolder] it will NOT see it.
The video is <HERE>
http://youtu.be/akFXXpz21roA workaround is to do this manually:
Run the .RWP
Run the installer.bat (to at least create the new engine folders)
Abort the installer before the last step (when it deletes the \Temp folder)
Manually copy the contents of the temp folders (everything inside Temp\Croft, Temp\Cyborg, Temp\004-4 etc.) into the newly created repaint folders.
Or move the unpacked BR189Pack01 folders (Audio...RailVehicles) to RSC\BR189Pack01\