I have installed Loki 0.4 (64bit) and am running it successfully. However I am now experiencing problems downloading apps from the AppCenter. I successfully downloaded several apps, but now it seems as if any new requests for downloads are stuck in a queue. After selecting an app for download I encounter a "Waiting for package manager lock" message. I currently appear to have 5 apps attempting to download. The apps included Darktable, Gallery, gThumb, Image Viewer, and RawTherapee.