I don't know how I locked "view offset", but how do I unlock it? When I attempted to navigate within the 3D viewport by using the CTRL-numpad options, it didn't seem to work, and I noticed a message in the communication part of the main header that gave the usual warning sign (an exclamation point within a red edged yellow triangle), followed by the text "View offset is locked". The warning appeared and closed so quickly I was not able to obtain a screenshot.

I don't know what I did to cause this, and cannot find any information in the manual or other Blender documentation about this warning message. How do I unlock the "viewport offset"?
Check the "view" panel in the properties shelf of the 3D viewport. This error message can be caused if the user attempts to move the 3D viewport when there is an entry in the "Lock to Object" text box.