This message has the following cause and solution:
The VSS Integration Component of Microsoft Access adds a setting to the SRCSAFE.INI file when you add a Microsoft Access database to the VSS server database. This entry flags the files in the VSS database as belonging to a Microsoft Access database integration project, and it looks similar to this:
[$/Northwind]
Disable_UI = Yes
This .INI file entry prevents you from using the VSS Explorer to check out the Microsoft Access database files. This is by design because the files are textual representations of Microsoft Access objects that you should only manipulate in the context of a Microsoft Access project.
In some cases, it may be necessary to perform operations on Microsoft Access objects from within the VSS Explorer. If so, close VSS Explorer, remove or remark the Disable_UI line in the SRCSAFE.INI file, and then reopen VSS Explorer. Then you will be able to perform the desired operation from VSS Explorer.
Note that when you reopen the Microsoft Access database, the VSS Integration Component (ACCSCC) adds the Disable_UI = Yes line back to the SRCSAFE.INI file. You can also add the line back to the file yourself.