Hi,
I don't know if this will help as I've never come up against that screen at all, and I'm wondering how you managed to get it!
I install downloads in the Package Manager straight from my desktop, I never start Rail Sim to do it.
Double click on My Computer, the disk which has Rail Sim on it, then program files, Rail Simulator, Packager, and then inside that folder double click on Package Manager.exe, a wizard then appears to take you through the process.
Once that has finished, then start Rail Simulator up to complete the process in the Free Roam editor in one of the routes.
Hope this does help,
regards from an Old Chap.