850
The following diagnostic is generating:
Business Use of Home #{PrefixNum}: Sent to invalid form.
Solution:
On Detail screen 29 'Business Use of Home' the 'Form (Ctrl+T)' and 'Activity name of number' (Ctrl+T) needs to be set to existing Forms and Activities. If the 'Form' and 'Activity name of number' does not exist they will need to be created.