If you set a fixed recipe (possibly even a normal recipe) on an assembler who's surface condition does not match the surface it's currently on, then the machine will work but crash when you try to open the gui. For example a recipe that needs pressure, but you put it on a space platform.
I also can't reproduce it reliably, after fixing the mod's relevant code (removing the surface condition) the machine was fine even after adding the condition back.
The error in the crash log only describes the machine, and that it was a gui opening event.
Setting a recipe on an assembler with an invalid surface condition
Re: Setting a recipe on an assembler with an invalid surface condition
Post the log and the save please, see 3638.