Solve Block Error!

A solve block never returns an error saying no solution was found for a specific variable, Actually, in MC12 and later a solve block never returns any error other that the useless "this variable is undefined", but if it did return a valid error it would be simply that it can't find a solution.

Anyway, the first thing you need to do is get rid of all the unnecessary equations in the solve block. For example, you have naphos=naphos6, and you do not solve for naphos. So above the solve block just assign naphos6:=naphos. You also have naphos7=naphos6, so you can get rid of that too. And you have naphos=nahos7, which, given the other two equations, is not an independent equation and should not be there. There are many more like these.

Once you have done that for all the variables that are equal, it would be a good idea to pick one variable name for each, and substitute that into all the remaining equations. Then check whether that leaves you with more redundant or non-independent equations that can be eliminated. The more you can simplify the solve block, the easier it will be to find the real problem. Right now, with all those variables with multiple names and non-independent equations in there, it would be almost impossible. it's not even possible to know if the number of equations you have actually matches the number of unknowns you are solving for.