As koz indicates, most of these issues happen when Audacity tries to access a project (database) over a network drive. It does not work reliably.
The “Failed To Open Database” error can occur if your database is corrupt. First transfer the .aup3 project to a local drive. If the error still occurs, it may be possible to “repair” the project. To do this, follow the steps outlined in the first post here: Corrupt or Otherwise Broken Audacity Project Recovery