Hammer error?

[Sdävtaker]

Hello,
I was doing some backup from Machine0 to Machine1 using hammer
mirror-copy and got a suppicious new file called "hammer.core".
Looking around the files it looks like a success copy but i still
curious about this new 720kb file.
Someone can tell me if i need to worry about it and where can i start
checking for errors in case there was one?
Machine0 has DFBSD2.2.0-release, Machine1 has DFBSD2.2.1-release,
could it be the problem? should i just upgrade both?
Sdav

-- 
Sdävtaker prays to Rikku goddess for a good treasure.