When you copy a project to a new folder, you should
Clean (or
Build all) to get rid of any leftover pointers to the old files. Until you do that, the linker appears to get confused, complaining about what looks like duplicate copies of the object files.
[Edit
Oh! You're not supposed to declare variables in .h files. The
bool ReleasingBall; line belongs in custom_routines.c instead, and what goes in custom_routines.h should be
extern bool ReleasingBall; (though I'm not sure where
bool is defined).