Creating a Custom Picker

Here is an article on how to create a custom picker: https://www.premierpointsolutions.com/training/help-and-how-to-articles/create-a-custom-picker-in-sharepoint-2010/

Opening the downloaded sample code will produce this error: Solution file '%s' cannot be migrated because the solution cannot be checked out from source code control. To migrate the solution, make sure the solution file can be checked out and re-open it.

The solution is to remove the READ ONLY attribute of all of the files and folder.