We have just released OpenSolver 2.7.1 which fixes a number of bugs in the 2.7.0 release. Please upgrade to this version if you are using 2.7.0 (or enable the update checker in OpenSolver to get automatically notified of these changes!).
Note: Unlike earlier versions of OpenSolver, we now correctly pass to the solvers (including CBC) the “Maximum number of iterations” value in the Options dialog. Be sure to set this (and the time limit) to a large value if want to find optimal solutions.