Due to the change of database management (XML + JSON) in the User Material Libraries, libraries created in previous versions of XSMP are incompatible with XSMP v.5.x. However, library conversion is very simple and automated, with two steps.
In XSMP Settings, select Manager > Legacy Library Converter. Then specify the root library directory. The library will be converted automatically, the new required files will be created and the old files will be moved to the Backup directory.
The next step is to specify the root directory and rename the library in the Manager, as you would when creating a new library. Please watch the video below.