Thank you. I have replaced the MessageBox() calls with LOG() calls.
About killing EXCEL... OfficeAutomation began many years ago and was made in VBA . Years later I moved it to C++ in U++. All this time from Visual Basic to C++ it was not possible to remove that problem.
At least only one EXCEL.exe thread is launched per program.
The problem of killing EXCEL is that we can kill other EXCEL process instead of the one created by the program.