The error message "MSB1009: Project file does not exist" indicates that the project file for the database project cannot be found. This could be due to a few reasons, such as the project file being deleted or moved, or the path to the project file being incorrect.
To fix this issue, you should ensure that the project file exists in the correct location and that the path to the project file is correct. You can also try running the command from the directory that contains the project file.
If you have already fixed any issues with capitalization and removed any duplications, then the issue may be related to the path to the project file. Double-check that the path is correct and try running the command again.