This message has the following cause and solution:
You are creating a database from the source code control provider, and the source code control provider project includes an .acb file, or you are checking in the .acb file, or you are adding the .acb file to the source code control provider.
No corrective action is necessary. Just remember to check out the Data and Misc. objects before making changes to tables, relationships, data access pages, command bars, database properties, or import/export specifications that you want to be saved.