Long story so if you are not easily amused by the process skip to the last two paragraphs!
Interesting editing problem occurred in our organization. We are in the process of migrating to an enterprise GIS, ,meanwhile our data is stored in file geodatabases. ArcGIS 10.2 for Desktop – Advanced 10.2.0.3348
I suddenly started having file access issues when attempting to start an editing session. I don’t edit every day and sometimes a week or more will go by between editing sessions. I checked to make sure that the file was available for editing (no one else was editing the dataset and in fact no one else was even viewing the data and there were no trailing file locks). In the same MXD I was able to edit a different dataset (stored in a different geodatabase). Hmm, must be a problem with the data. Ran a check geometry and still had a problem. Exported the data problem solved. OK PITA but stuff happens. Then it happened with another file! Then my coworker started noticing a problem too, but not with all files. He did some searching and found that if you have the same Geodatabase connected to your MXD in two different ways (one added through an ArcCatalog file connection and one added through a windows mapped directory but both layers exist in the same geodatabase) will cause a schema lock and which prevents editing. OK so I checked my data and reset the sources of my layers so that they all matched. That seemed to solve the problem but what a pain. Now I have to check all of my MXDs. A couple of days later and . . . problem again but with a different MXD. Grumble, grumble, grumble, I’ll edit later, I have to print a map for someone on the fly. I need to add a layer to my MXD and while navigating to the file realize that there are no folder connections…hmmmm. All of the data loads, views queries etc just fine even though the folder connection is missing in ArcCatalog. I recreate the folder connection and viola! I can edit! I closed the MXD and opened the original MXD in which I had experienced the editing issue and could immediately edit! A couple of days later IT either pushed out or retrieved a couple of extensions and I started having the problem again. Looked in ArcCatalog and sure enough my folder connections were missing again. The interesting thing is that Windows file explorer mapping was recognized so anything that was solely attached through a Windows File Explorer mapping was golden.
Bottom line: datasets may be attached through two different paths in the same mxd and still allow editing. If Arc folder connections get dropped (which may randomly happen with software updates) apparently ArcMap can still find and use the data previously defined in an MXD but you can’t edit the data until you add the folder connection in ArcCatalog.
In the attached jpg I have highlighted two data source connections for the same geodatabase. The first one is an ArcMap\Catalog folder connection and the second is a Windows File Explorer directory mapping.