I have a corridor that creates 3d lines ie Ditch Flowlines. I want to extract them back out to an alignment with profile. What is the best way to get that information?

It says it's not a valid object to offset.  I've tried copying it as well.

Try the offset tools under horizontal geometry  I have used the offset tools to create point control alignments for corridors etc..  Should be able report on the geometry.  May need to create direct offset from control line instead of corridor feature. Then set your corridor as active profile for the feature. 

Plan by 3d element just reports that the reference is a read/only reference.

Using which tool seems to be my issue.  Copy element just reports that the element in the corridor is invalid.

Robert,

You could reference in the corridor in a new 2d file and create a new geometry feature with a horizontal and vertical offset of 0.0' from the ditch feature. (Turn your create 3d button on to create the vertical automatically)   Then you could remove the rules.  Should be able to export this to alg or gpk file.