Error -2147213296 (RefreshPDMDropDown)

Symptoms:  When attempting to open a project you get the following error:

Error in Object: RefreshPDMDropDown

Error Description: Value item allready exist or can not be added

Error Number: -2147213296  

Cause: There is likely a duplicate location type, location or zone. 

Solution:  In the Project Grid, right click on a project that is having the issue and select Display Project Information and then press the Edit button and look through your locations and zone for duplicates.  Very often this happens when there is a duplicate “Unassigned” location or zone.