I am also experiencing similar problem with RTL-SDR on a new computer with WIN10 . I have installed Multipsk 4.38 outside "Program" directory and it in general works fine, it also accepts "Direct input" from a Funcube dongle.
I also spent some time to get the RTL dongle working with SDRSHARP (Zadig etc,) but now it works fine. So actual situation is:
MULTIPSK + FUNCUBE : OK
SDRSHARP + RTL : OK
MULTIPSK+ RTL: PROBLEM
When I try to set "DIrect input" from RTL I get an error window saying "problem on a rtl dll" and then lists rtlsdr, libusb-1.0 and msvcr100. I just tried to replace above dll's with the ones currently working in SDRSHARP but no success.
Any suggestion on thingsd to check? Thanks. Mauro