The NavWorld operation didn't complete successfully and produced no usable result.
An invalid NavNode most often causes the failure. The node was important for the operation either because it was given as an input parameter, or because the operation stored it inside a NavQueryBuffer at a time when the node was still valid. In these cases the NavQueryStatus value has the NavQueryStatus.InvalidParameter flag set.
Another cause for an operation to report a Failure status is a NavQueryBuffer object used as input although it isn't in the correct state that the operation expects it to be. As an example, a call to NavWorld.ContinueFindPath needs as input parameter a NavQueryBuffer that has been initialized correctly in a call to NavWorld.BeginFindPath, otherwise the pathfinding operation can't continue.