Typically, an error or problem deleting a database field is due to one of two scenarios.
The database field is used in an index
Navigate to your Indexes, and make sure that this column isn't used in any of your table indexes. If it is, you'll have to adjust or remove your index to no longer utilize this database field.
Your database storage is full
When your database storage reaches capacity, you'll find that making changes can result in an error. Reach out to Support and we can help get you up and running again.