I find that I'm getting this error quite a bit. Mostly when working with Mosaic Datasets, but also with other geoprocessing tools. The data is stored on a network location. No one else is accessing the data. I'm not sure why there is a lock in place. In the past, I've been able to get around this by using the ArcPy command line. That works maybe 50% of the time.
I just tested this by creating a new File GDB and then attempting to create a Mosaic Dataset within the GDB. The GDB had never touched, and still I get this error. Is this because I'm accessing a network drive? This is the same location that I work in when in ArcMap 10.1, and it works fine from there.
Also, I've noticed that about half of the time, Mosaic Datasets aren't even visible from the "Add Data" window.
Can anyone shed any light on the situation? Why are these GDBs locked? Adding vector data from file GDBs doesn't seem to be a problem, but mosaic datasets are very problematic. I've upgraded to ArcGIS Pro 1.1.1, and this is still happening.
Edit: It looks like the Create Mosaic Dataset tool gets as far as creating the AMD...CAT catalog file within the GDB before it fails.