Projects that use Constraints (axes constraints, multi-photo constraints or control points) can fail processing if the constraints are incorrectly defined or in the case of control points, incorrectly marked.
If this project has multiple photos and is using constraints, try reprocessing with Constraints turned off (second tab of the Processing Dialog). See the Troubleshooting Constraint Processing Problems section for more information.
If the project fails to process with Constraints off also, follow the questions in the Constraint-less project path of the troubleshooting.
The main reason control-based projects fail is because of incorrect control points. The problem can either be incorrect x,y,z values, incorrect marking of control or misreferencing of control to the wrong photo point.
Sometimes users can spend a lot of time trying to figure out why a control based or Inverse Camera project will not process because they adamantly assume that the input control points (perhaps supplied by a surveyor) are correct. Make sure you verify that all the x,y,z values of the control points are correct and that they are marked correctly on the photographs.
For Inverse Camera work also check the starting camera parameters. Perhaps they need to be closer to the final solution. Try changing the values of format size, principal point and format size a bit to see if it will solve. Also try solving for just one of the parameters instead of all of them.