When I switched to PSSUITE, my computer prompted me to install a separate set of drivers. Aside from the ones installed by the PSVita content manager. Maybe try a different USB port then make sure it installs then try transferring.
Maybe it's worth mentioning that I also have the full sdk downloaded which can be found by googling vita sdk (it's around 300mb).
Weird, the app doesn't find my vita when i am in the developer. but if i minimize it then the app finds the vita. but i try and connect and select upload and it doesn't work, but then i go back into the vita connector and select refresh then the vita disappears and doesn't have anything connected. i did follow the guide and can't get it working, anyone got any ideas?