Error during mission execution

Hello all,

I have used pix4d capture for a number of missions, and until today, ive not had any problems. I have added a screenshot, to show the issue im having. Following my first battery swap, the planing dashboard displayed an error message, and the drone would not fly. Has anyone seen this before? What does "unknown " mean, ( see top right corner of the image)and how can i fix it to continue the mission? Thanks for the help.