Column is the full-text filter for columns that participate in full-text indexing on a table.

You are trying to delete a column or change its data type, but that column is the full-text filter for one or more other columns for which a full-text index exists.  If you proceed with the operation, the columns will no longer participate in the full-text index.

If you later want to reestablish full-text indexing for these columns, you must choose or create a new full-text filter field, and you must add these columns back to the full-text index.  For more information about accomplishing these tasks, see Full-Text Indexes.