This error may be caused by a high start date or end date on one of the constituency codes on the constituents record. To check the constituency code start date follow these steps
  1. Click constituent > constituent search
  2. Search for and select the constituent 
  3. Click on the personal Info tab
  4. Under the constituencies sub-tab make sure none of the start or end dates have a high value like 9999
  5. If they do click on the drop down arrow next to the constituency and click edit
  6. Adjust the date and click save