If you are having a problem with dragging files into Studio One, then more than likely you are running the program as administrator. Here is what you can do to resolve the issue:
1. Go to c:\Program Files\PreSonus\Studio One 4 and right-click the Studio One.exe file.
2. From the right-click drop-down option, go to Properties>Compatibility and un-check the option to "run this program as administrator."
3. Close and re-open Studio One. The problem should now be resolved.