Tried to create a column in my list called “UniqueId” today.
The column creates just fine, and works within the UI. However, if you try to programtically update the value SPListItem[“UniqueId”] — You’ll quickly get an error.
This is because SharePoint realized that UniqueId was actually already in-use by the system, and named your column something like UniqueId1.
To find out what your actual field is named, go to edit your column and look at the end of the URL in the address bar. You should see your field name there.