fixed by a fork

I have this exact problem as well. The full error text I am seeing when running the full Attempt is:
/home/codewarrior/program.fsx(89,6): warning FS0058: Possible incorrect indentation: this token is offside of context started at position (83:6). Try indenting this token further or using standard formatting conventions.

/home/codewarrior/program.fsx(96,5): warning FS0058: Possible incorrect indentation: this token is offside of context started at position (89:6). Try indenting this token further or using standard formatting conventions.

/home/codewarrior/program.fsx(103,5): warning FS0058: Possible incorrect indentation: this token is offside of context started at position (96:5). Try indenting this token further or using standard formatting conventions.

/home/codewarrior/program.fsx(55,17): error FS0039: The value or constructor 'Dictionary' is not defined. Maybe you want one of the following:
dict

Ah you're right - I fixed the signature of the solution.