SQL Server 403 Error When Setting a Geography Type for Update - sql

Question

All I need to do is simply get one geography value from a table and store it in another table. There is some logic for which row to take from the origin table so it's not just a straight select.
In any of 50 possible variants of this, I get this error when hitting the update to the target table:
Msg 403, Level 16, State 1, Line 1
Invalid operator for data type. Operator equals not equal to, type equals geography.
My SQL looks like this at the moment:
declare
#EquipmentId int
, #CurrentLocationId int
, #CurrentGeoLocation geography
, #LastUpdated datetime
select #EquipmentId =
(
select top 1 EquipmentId
from Equipment
order by EquipmentId
)
select #CurrentLocationId = (select top 1 EquipmentLocationId from EquipmentLocation where EquipmentId = #EquipmentId order by LastUpdated desc)
select #LastUpdated = (select top 1 LastUpdated from EquipmentLocation where EquipmentId = #EquipmentId order by LastUpdated desc)
UPDATE
dbo.Equipment
SET
CurrentLocationDateTime = #LastUpdated
, CurrentGeoLocation = (select GeoLocation from EquipmentLocation where EquipmentLocationId = #CurrentLocationId)
, ModifiedBy = 'system'
, ModifiedByUserId = -1
, ModifiedDate = getdate()
WHERE
EquipmentId = #EquipmentId
I have had CurrentGeoLocation set in a variable of the same type, selected into by the same statement you see in the update.
I have had an #CurrentGeoLocation variable populated by a geography::STGeomFromText as well as geography::Point() function call.
I've used Lat and Long variables to call Point and FromText functions.
All the same result, the above 403 error. I could understand it somewhat when I was concatenating various permutations of the GeomFromText function that needs well known text format for the point parameter, but field value to field value is killing me, as is the fact that I get this error no matter how I try to give the origin point data to the target table.
Thoughts?
Update:
I've been experimenting a little and found that the following works just fine:
declare #GL geography
select #GL = (select GeoLocation from EquipmentLocation where EquipmentLocationId = 25482766)
print convert(varchar, #GL.Lat)
print convert(varchar, #GL.Long)
update Equipment set CurrentGeoLocation = geography::Point(#GL.Lat, #GL.Long, 4326)-- #NewGL where EquipmentId = 10518
But then when I apply this plan to the original script, I'm back to the same error.
The data in the test is working off the exact same records as in the original script. The original script is working off a collection of EquipmentIds, on the first one, I encounter this problem. The short test script uses the same EquipmentLocationId and EquipemntId that are the selected values used to update the first Equipment record in my collection.

Answer 1

Solved!
The error had nothing to do with the geography type as SQL reported. By pulling items in and out of the update statement in an effort to isolate why I still get the error even if I save everything but CurrentGeoLocation and then another update for the geography, I found that CurrentLocationDateTime (datetime, null) was the culprit. Deleted the column, added it back. Problem solved. Original script works as expected.
Don't know what happened to that datetime column that caused it to throw errors against a geometry type, but it's fixed.