This tutorial is courtesy to Jeffrey Pinheiro, aka “The Revit Kid” and his post ‘I can’t select my link‘.
In Revit 2014 there was a new icon introduced in the bottom right which allows you to lock all linked Revit models. If the icon is accidentally checked, it can be an incredibly frustrating experience to try and figure out why you can’t select anything. Like me, you’ll probably check the usual suspects: worksets; design options; visibility settings; etc. but to no avail. But you’ll be looking in the wrong location. Rather, you should go to one of the following locations:

- On the ribbon, under the Modify tool, click Select to expand the drop-down menu.

- Click an icon in the lower right corner of the status bar.
For more information on the tool’s functionality, check out Autodesk’s help page on the topic and their video tutorial.