I got the same java error as erikandash and finally figured out why. Seems like I (inadvertedly) edited the API-key in the CP web-ui when I marked (highlited) a section of the key. The leading "b" was moved and inserted in anathor position. I then entered this altered key in nzb360, and it worked !!! However, after restarting CP I got the error message. After checking my settings again I found that the API-key in CP had reset to the original (default) key, so I had to edit the key in nzb360 to match it, and voilá :)

So, I reckon it's a bug in CP web ui. You shouldn't be able to edit the API-key, or - if it in fact is a feature, it shouldn't reset after restarting.