MrZeno: I think it is to do with GalaxyCommunicationsService.exe needing to be running. Try starting it manually and then try Hammerting... working so far, but not ideal.
The game launches and seems to run fine as long as Galaxy is, at minimum, a background process as shown in the system tray. The full Galaxy desktop environment does not need to be running to successfully launch Hammerting.
I avoid using Galaxy, and rarely allow it to run on my system - only in cases where standalone patches are not available to fix critical issues (e.g., game stopping bugs). And even then, I try to limit Galaxy runs to times only when it is necessary. Like now. As soon as a patch hits to fix this issue, or I abandon this game in favor of another that doesn't require Galaxy - whichever comes first, I will again carry forth without Galaxy.
/soapbox
Galaxy should not be required to run a single player game, and if it is, then that is contrary to advertised information on the game sale's page. I'll concede that it may be required for multiplayer as with many other multiplayer enabled versions of GoG titles, but the presence of Galaxy communications should not be required solely to launch the game. Its presence should only be verified upon the user selecting and pursuing the provided multiplayer option after the game is launched. In the best of worlds, even if Galaxy was not enabled prior to launching the game, the game should be able to enable Galaxy communications in the background before proceeding to multiplayer options.
/soapbox off