I use Arena for want of an alternative GUI to play a game of chess. I use the tournament to test engines to make sure they are working ok before I play one a few games. I have noted that many engines including x64 build don't seem to work properly. This seems to occur more less so with 5 pieces Nalimov tablebases.
For as I can tell from the manual for UCI, an engine needs to be threaded to a degree to be responsive to command from a GUI. It seems that the lag enumerating tablebases is causing Arena to think the engine is kaput.