Let's take this one step at a time. So, you're downloading .nzb files from NZBMatrix and trying to import them to the queue. How are you trying to do this? By putting them in the autoimport folder, or by double-clicking them, or manually from the NZB button on the main toolbar?
While you're figuring that out, please take 5 seconds to open one of the .nzb files in Notepad and make sure it's valid xml.