Are you trying to open a project with the xml extension in BAS? Probably your project is damaged, you did not edit it manually using text editors? Try to restore it from backups located here:
C:\Users\User\AppData\Roaming\BrowserAutomationStudio\projectbackups
@BasUser110 a mask is not a data type, but a url mask. The url does not have to contain a file extension. You need to look at which queries load this data and write a mask for them.
