Typically when the game crashes or has an error, like locking up and not allowing you to proceed, a traceback.txt file is generated that details info on the error. Since in your original post you neglected to provide any additional information like what version you have, what type of system you're playing on, etc. It is the easiest way to look for information about errors and what may have happened to cause them.
Full traceback:
File "game/script.rpyc", line 1362, in script call
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File "game/loc_workout.rpyc", line 3792, in script call
i i *w@Z 䠭r U G U U6 D * G}e e d U Z EZ *" * C M Ov d E3 UN ]IcZ n dy= *I s B& r ; NSq q r \ r E=K w S SG J^' G T (r JTf U A <S dU [ g "LW & H Q f > * Z# U֡ U6 Q[ <<Z r/e d U ' yWy ZfFZ |*" * G ' U.@ *gEZ "ҘV X^ [^ JR * Ib GŝEq Uq 3
File "game/loc_workout.rpyc", line 7230, in script
r6 Бh d T 4* h D q2 ,O bD; [ v H1
File "renpy/ast.py", line 1191, in execute
show_imspec(self.imspec, atl=getattr(self, "atl", None))
File "renpy/ast.py", line 1148, in show_imspec
expression = renpy.easy.displayable(expression)
File "renpy/easy.py", line 111, in displayable
raise Exception("An empty string cannot be used as a displayable.")
Exception: An empty string cannot be used as a displayable.