Hi @Matej_Cervenan,
On the Community, we have another thread about the same problem. Please have a look at Error e0400b: Invalid Format.
If you used only one version of Pix4Dmapper to process the project, the problem could be caused by the files that somehow got broken.
We can verify that you for as soon as you send us the .log file and .p4d for examination.
Regards