I am pretty sure that I have the new field set up correctly but when I "check challenge" it throws an exception. 

https://developer.salesforce.com/trailhead/force_com_admin_intermediate/point_click_business_logic/roll_up_summary_fields

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. 
java.lang.IllegalArgumentException: unable to find field dataType for complex reference
unable to find field dataType for complex reference 
Contact your administrator for help.: []

I am pretty sure that I have the new field set up correctly but when I "check challenge" it throws an exception. 

https://developer.salesforce.com/trailhead/force_com_admin_intermediate/point_click_business_logic/roll_up_summary_fields

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. 
java.lang.IllegalArgumentException: unable to find field dataType for complex reference
unable to find field dataType for complex reference 
Contact your administrator for help.: []