Anyone else have problems with the hammer? Literally every time i throw it at someone i get an error message about steam achievements or somthing.

Yeah, unfortunately the GoG edition is.. also the steam edition. We have all the programming for the steam achievements in our build, and whenever we meet the criteria for an achievement we're getting bugs. Usually you can 'ignore' the bug, but I have had this crash me once when achieving the 'two kills with one brick' the first time.