Affected versions: Smart Styles version 3.0
Affected platforms: All compatible platforms

Problem
My Smart Styles library has become an Object Library and I am not able to change it back to a Smart Styles library.

Analysis
One of the reasons why a Smart Styles library can turn into an Object library is when a style from the library has been applied to a table.

Work-around
If the above is is true in your case, try to apply the style to the text frame that contains the table rather than applying it to the table itself.

Resolution
Restart InDesign.

This issue has been resolved in Smart Styles version 3.1.