I have a SharePoint list that I created by uploading it from an Excel file.
We are trying to query with the GetExternalValue in a web form, however the query is returning a blank string when it should be returning something else.
The issue appeared after adding an extra column from with in SharePoint.
Foundation 11.x.x and 12.x.x
It seems that SharePoint only accepts changes to SharePoint lists via the same method of creation.
If an excel upload was used to create the list then those new changes should also be done via updating excel and upload.
If you have uploaded the the SharePoint list via an excel then also make sure you add the extra columns to the excel and upload again for it to work.