Object reference not set to an instance of an object

[aedwardsQM7YG]

Whenever I try to open certain files in civil 3d it'll pop up this message and it will keep re-appearing after I click continue which blocks me out of the program.  Here is the error message that pops up:

System.NullReferenceException: Object reference not set to an instance of an object.
at Autodesk.AutoCAD.LayerManager.LayerManagerControl.UpdateConfiguration()
at Autodesk.AutoCAD.LayerManager.LayerManagerControl.UpdateLayerManager(RestoreType eRestore, Boolean bForce)
at Autodesk.AutoCAD.LayerManager.CommandCatcher.UpdateOnIdle.OnIdle(LayerManagerControl lmc)
at Autodesk.AutoCAD.LayerManager.LayerManagerControl.Application_Idle(Object sender, EventArgs e)
at System.EventHandler.Invoke(Object sender, EventArgs e)
at Autodesk.AutoCAD.ApplicationServices.Core.Application.raise_Idle(Object value0, EventArgs value1)
at Autodesk.AutoCAD.ApplicationServices.Core.Application.OnIdle()

[Nilesh_Chaudhari]

@aedwardsQM7YG ,

Did you try Purge and Audit? 

[aedwardsQM7YG]

It wont allow me to use commands. 

Update: I've found the issue is caused when the "Layer Properties" button is clicked in the toolbar or when you open up the new layer property palette.

[mzjensen]

I just started getting this error yesterday as well. Currently only happening on a single drawing, not all of them. When I open the culprit drawing, it gets stuck in an infinite cycle of unhandled exceptions, so I have to force quit via Task Manager. The only thought I have is that this drawing has a reference template attached.

When I try to Recover the drawing, there are a few errors that it finds and fixes. But the unhandled exceptions continue to occcur.

[tcorey]

If you create a new drawing, are you able to INSERT the problem drawing?

[mzjensen]

@tcorey yes, that works. 

[mzjensen]

The issue was solved for me by uninstalling the 2020.5 update. Sounds like it is pretty buggy.

https://forums.autodesk.com/t5/civil-3d-forum/civil-3d-2020-5-update-is-on-hold/td-p/9788841