When reconciling a version in Geodatabase Manager, either solely for a reconcile or during a post operation, the reconcile fails with the following type of error in the GDBM logfile:
1/21/2016 2:54:19 PM : Error reconciling version ADAMS.SN_56904: Object reference not set to an instance of an object..
This error is thrown if the VBA component of ArcGIS is either uninstalled or damaged.
If the VBA component is uninstalled, reinstall it. If the component is already installed, perform a repair install on it from the Programs and Features item of the Windows Control Panel. Ensure that the VBA installer used is the one distributed with your current version of ArcGIS and not an older installer from a prior ArcGIS release.