Excel Solver - Lower and upper bounds on variables allow no feasible solution (20).

This message appears if you’ve defined lower and upper bounds on a decision variable, where the lower bound is greater than the upper bound. This (obviously) means there can be no feasible solution, but (depending on the Solving method) Solver will detect this condition before even starting the solution process, and display this message instead of “Solver could not find a feasible solution” to help you more quickly identify the source of the problem. If you have defined your bounds and other constraints in uniform blocks, the lower and upper bounds on a given range of cells will appear consecutively in the Solver Parameters dialog outlined list (where they are grouped and sorted), making it easy to spot the inconsistent bounds.