When trying to perform any kind of function in MSC (restore, repair, etc.), the structure file (.4DB or .4DProject) must be accessible somewhere on the computer in order to gain access to MSC. In rare instances where the structure file gets lost and only the data file (.4DD) remains, no possible data restoration will be able to be performed as the structure file contains important key info like tables, fields, indexes, and etc.

Be sure to keep the structure and data file easily accessible at all times in these scenarios.