I stumbled a few times over this bug but now, I think I know what's causing it.
When including a NZB with a long name (in my case 188 letters) the file are downloaded into the tmp-directory, but AltBinz does not decode, though it is saying so.
One glance a the log-windows -- one message gets repeated all over again:
[23.03.2008 16:18:13] [Dec] Exception Cannot create file "". Der Dateiname oder die Erweiterung ist zu lang
This is annoying because Alt.binz keeps downloading the other files but is not decoding even one. But I think a solution is easy, because all one need to do is to rename them.
BTW: I am using 0.27.2.