Xref not in Project Issue

[StanleyMechanical]

I have checked the forum for answers to the following but none of them seem to apply or work.

I modeled a vessel using AutoCAD some months back and am trying to use it in a current project im working on. I converted the model to a Plant 3D model and attached nozzles where applicable. I then copied the drawing to the project and it now shows up under a folder called "equipment" within project manager, as expected. The problem occurs when i try to xref the drawing into a piping drawing, which is also in the project. The vessel can be seen in the piping drawing but there is no intelligence or functionality associated with it. When the cursor hovers over the vessel, it shows "This xref is not in the project....etc".

As a test, I put some piping directly on the vessel, within the vessel drawing itself. I then detatched the vessel from the piping drawing and re-attached it. The Plant 3D piping does not show up on the xref either.

I have checked the path type, and changing it from absolute to relative seems to make no difference. This was suggested in a seperate thread.

I am obviously missing a trick or setting somewhere.

Any suggestions?