Same here, it just happened?
I merged 96 small projects, photos acquired by eBee so each project is small, total number of photos is just over 10,000.
After merging, over 60% of my calibration was gone even those each individual project was nicely calibrated over 95 of the images. So I decided to “Reoptimize and rematch” ran for 12 hours, then froze after a completion status and asked me to generate report if I wanted. But I could not generate report as the whole PC froze. So I decided to hard reboot. Then when I opened the project again I got the error as shown below.
I then decided to go into the file itself (project file) and double click to open it, same error. Has anyone found a solution please? Pix4D Support, I see no more comments after July 27, 2016.