Solved
The error messages from solve blocks are useless. There is only one: "this variable is undefined". You get that even if the problem has nothing to do with undefined variables.
In your case there are two immediate problems. First, your functions IFC1, IFC2, IFC3, IFC4 are undefined. Second, you have 8 equations but you are only solving for 5 unknowns. The number of equations must be the same as the number of unknowns.

