Normally, _ITERATOR_DEBUG_LEVEL is set automatically by choosing either the Debug or Release build mode. So when you meet this error, it may well be that your projects in your solution have different build modes ( one is Debug and the other is release ) . You can have several solutions to fix this problem.
The first solution is that you can clean the error projects and rebuild them. Remember to build them in the same build mode. If this solution cannot help, you can try the second solution.
The second solution is that you remove the error projects, and create new projects, add source files of removed projects to the new projects. Rebuild all removed projects with the same build mode.
I solved this problem with the second solution, and I hope it also works for you
