I have a layer file that loses the path to the source on some files (in other words, you get the little red ! next to the layer in question). In the case this morning the source path was still there and correct. I just clicked on “Set Data Source” and clicked the feature class that it was already pointing to and it worked.
All of the other feature classes link up correctly – even ones that are in the same File GeoDatabase. This layer file was created yesterday.
I’m using ArcGIS 10.3.1 on a Windows 7 machine. Though this has happened sporadically back through at least 10.0 – it is just annoying enough now that I figured I’d put out a query.