I am getting the below error message when submitting a specific quiz. This is not occurring on every quiz, but on a specific one.

Server Error in '/' Application. Method not found: 'System.String Elearningforce.SharePoint.DB.ListInfo.get_FieldsSchema()'.

Solution:

The reason of the error is a mismatch between lms and common solution versions. The issue occurs when you're using SPLMS ver. 3.2 which is dependant on a lower common ver. <=1.0.0.76, but you're running a higher version of the common solution. 

To fix the problem it’s necessary to upgrade to lms version which supports a higher version of the common dependency solution, that is SPLMS 3.3 which you acn find on the downloads portal.