Just to recap the situation, you were using the version 4.1.25 but then you want to upgrade to the latest version 4.4.12.
Unfortunately, at the time you wanted to upgrade, you did not hold the S&U any more (support and upgrade service) which does not allow you to update without charges.
Therefore when you tried to log in, it did not allow you to access the software.
So then you uninstall and re-install your old version and then you could not open your project. Is it right?
I would like to suggest you to re uninstall the software and make sure that you follow these steps:
- In the Search Windows type, type “program” and select Add or remove programs in the Settings list.
- Scroll to find Pix4D Desktop and click the application.
- Click Uninstall.
- On the path where Pix4D desktop (Pix4Dmapper) was installed (default is C:\Program Files\Pix4Dmapper), ensure this folder does not exist anymore. If it exists, DELETE this Pix4Dmapper folder.
- In C:\Users\pix4d\AppData\Local\pix4d, ensure the folder Pix4Dmapper does not exist anymore. If it exists, DELETE this Pix4Dmapper folder.
- In C:\Users\pix4d\Documents, ensure the folder Pix4Dmapper does not exist anymore. If it exists, DELETE this Pix4Dmapper folder.
- On windows the search bar type: regedit and then search for the folder stored in the path: HKEY_CURRENT_USER\Software\pix4d and make sure this folder does not exist anymore. If it exists, DELETE this Pix4Dmapper folder.
- Restart the computer.
- Then reinstall your old version.
Regarding the e0400b error, you might need to modify the *.p4d file:
- Open the .p4d file using Notepad++.
- Go to line 35 and set the OptimizerType to Ceres .
- On the menu bar, click File > Save.
Hope this will help.