Depending on their File Mapping settings in GoLive Web Settings, and other configurations, some Mac users have reported problems opening and editing the "domains.dat" and the "CatalogIntegrator.mysql.sbs" files in GoLive, especially when double clicking it in the site file. Sometimes, Macs will attempt to open these files in another application.
There are various ways to fix this. The quick and simple way is to, in the .site window, Control-Click on "domains.dat" or "CatalogIntegrator.mysql.sbs". This will open the Contextual Menu.
Then select "Open --> Open in Adobe GoLive". It should open in the GoLive Source Editor.
If you still find it trying to open in another application, Control-Click on the file again, and select "Open --> Show Properties", which will open the "Show Info" window, where you can set BBEdit, or GoLive as the application to open it. TexEdit Plus is another good one. (Apple's TextEdit 1.1 will not save the file under its own name, because it is unable to save a plain text file. We hope Apple will remedy this omission soon.)
Also, you can open Web Settings, File Mapping tab, and in the text category, add "dat". This should cause GoLive to be able to open these files from within the .site file.