In some cases, the error messages may be hard to understand. Below is the list of most probable reasons for such "confusing" messages:

Empty extent -  Bounding box is misplaced during Build Tiled Model or Build Orthomosaic operation and doesn't contain any information or all the cameras for the related area are disabled. 

Empty camera list - no cameras are pointing to the area of the orthomosaic generation.

Empty frame path - the selected operation (for example, import DEM) requires the project to be saved in PSX format.

Empty surface - Bounding box is misplaced during Build Mesh operation and doesn't contain any information.

Index Overflow - usually such a message is observed when the Arbitrary mesh generation method is used based on a very big dense point cloud. To reduce the number of points you can use Filter Dense Cloud option in the Tools menu or shrink the bounding box to the smaller volume using Region-related instruments in the Model view mode. As an alternative we can suggest to use depth maps based mesh generation available since the version 1.6. 

Null dense point cloud -  missing dense cloud for the operation based on it (like mesh generation or classification). 

Null model - missing mesh model for the operation based on it (like mesh decimation).

Null point cloud -  missing sparse cloud for the operation based on it (like mesh generation).

Media resource couldn't be resolved -  indicates that some video codecs are missing in the system, so we can suggest to install K-lite Codec pack or similar in order to guarantee the Import Video operation. Note that you do not need to install any auxiliary utilities in addition to the codecs themselves.

Some photos failed to align - the message indicates that some images were not aligned as a result of the adjustment process. This may be due to poor image quality or insufficient overlap. We can recommend you try to select images in the Workspace pane and select Align Selected Cameras command from the context menu.

Zero resolution -  Bounding box is misplaced prior to the Build Dense Cloud operation and doesn't contain any information (almost no tie points are present in the bounding box and therefore no depth maps can be generated).