Entity Framework error – Error 11009: Property ‘ ‘ is not mapped

I had this issue when I changed a column name from CampaignKey to CampaignCode. After making the DB change, I went to the .edmx designer, right clicked and chose Update Model from Database. Then when I compiled I got the error:

Error 11009: Property CampaignKey is not mapped.

Taking a closer look at my table in the designer showed me that Visual Studio had created the new field CampaignCode as in the DB. But it also had left the old field CampaignKey in there, causing the error as it no longer exists in the DB.

To fix the issue, I right-clicked on the CampaignKey field in my table in the designer and selected Delete.

After that I saved the .edmx, compiled and the error was gone.