Unable to cast object of type 'Microsoft.Xrm.Sdk.OptionSetValue' to type 'System.String'
if you facing OptionSetValue Cast error in your Plugin use this code to resolve the problem
OptionSetValue learnerAggrementoptionSetValue = guids.GetAttributeValue<OptionSetValue>("vwi_learneragreementtype");
if (learnerAggrementoptionSetValue != null)
{
int selectedOptionValue = learnerAggrementoptionSetValue.Value;
}