Error: Graph is being computed externally

Unexpected exit of Meshroom while processing can cause the "Graph is being computed externally" problem.#249

The Start and Stop buttons are greyed out.

Background: When Meshroom is terminated unexpectedly, files are left in the cache folders. When you open such a project Meshroom will think, based on the residual files, that parts of the pipeline are computed externally. (This feature is not included in the binary Release 2018.1.0) So the buttons are greyed out, because Meshroom is waiting for an external source to compute the graph. Obviously, this can not work.

To fix this problem, go to the cache folder of your project and delete the contents of the node folders for the nodes who starting with the node where Meshroom stopped working (marked in dark green). Now you can continue computing the graph on your computer.