It happens when you try to build an application (normally, .EXE). Entry point means your "main" function used by OS to start your application when it is loaded. It is indicated in few different ways, and, in some situations, more then one functions satisfy the criteria for being an entry point. For Microsoft systems, it is described here: http://msdn.microsoft.com/en-us/library/f9t8842e%28v=vs.110%29.aspx
You have your project; see by yourself where you could define a redundant entry point. Chances are, it happens after you got someone's code and modified it without full understanding. This is warning, not error, but you should work without any warnings. In this very case, the function
is likely not what you meant to use.