I am getting this error: Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_EXECUTE_FLOW_TRIGGER, The record couldn’t be saved because it failed to trigger a flow. A flow trigger failed to execute the flow with version ID 30150000000GzkN. Flow error messages: An unhandled fault has occurred in this flow
An unhandled fault has occurred while processing the flow. Please contact your system administrator for more information. Contact your administrator for help.: []

Code is:
public class ContactSearch
{
    public static List<Contact> searchForContacts(String St1, String St2)
    {
        List<Contact> ContctList = [select ID,Name from Contact where LastName = :St1 and MailingPostalCode = :St2];
        return ContctList;
    }
}

Please help!!