Spot Coordinate dimension can't touch some linked DWG elements

[anthonyB]

My DWG survey is linked into my Revit file.
I can use Annotate > Dimension > Aligned to place dimensions on Lines and Polylines in the linked DWG. This is good.
However Annotate > Dimension > Spot Coordinate only allows me to select some of the Lines and Polylines.

With my limited knowledge of Autocad I can see that all layers are On, Unfrozen and Unlocked. Hatches been removed and Blocks exploded.
The DWG survey has been "prepared" by (amongst other tasks) transposing all elements to near the Origin point, to be within the 20 mile limit.

When in Revit, even with a pair of two identical parallel Lines in the linked DWG, I can place a Spot Coordinate on one but not on the other.
Why might the be the case? What setting do I have to change? Is it in Autocad or is it in Revit?

Does it have something to do with the series of messages I get when I open the file with Autocad?:
* This DWG file was saved by an application that was not developed or licensed by Autodesk... (Continue)
* One or more SHX file are missing.....(Ignore)
* ...Proxy Graphics... (Show proxy graphics)


Thanking you in advance.

[Steve_Stafford]

Not all AutoCAD elements are real in Revit and a proxygraphics messages suggests 3rd party or smart elements are present. In the worst case those elements are not even displayed in Revit at all.

Sometimes exploding the elements in the DWG file is sufficient to reduce them to a basic AutoCAD element Revit does recognize.