I need some coaching for 3D constraints

I am attempting to understand the process of working with 3D constraints.  Note that I am quite well versed in the general topic, since I have used several other parametric 3D modelers.

My problem is that there is something in the process I must be omitting.  I start with a 3D template.  I insert a pair of mechanical components, i.e. a nut and a bolt.  Then, I attempt to constrain the nut and bolt together.  I did successfully create the co-centric constraint between them.

When I attempted to create a distance constraint between the face of the nut, and the face of the bolt.  I do successfully initiate the process by selecting the distance constraint icon, then I successfully select the two faces.  But, I always get the error, "Invalid Selection".   Note that I did a little playing around between the co-centric constraint, and when I attempted the distance mate.

I suspect I somehow got out of the proper mode.  My guess is that it is sort of like being inside the dimension creation mode.  If you attempt to create a dimension outside of that mode, it does not recognize the command you are typing.  Did I get out of the proper mode for 3d constraints?

Attached is a full screen grab after the error occurred.  This may provide a clue to someone about what is happening.

As an aside, while there are a few tutorials in the online help area, and some videos, I wish there were more.  Perhaps I need to purchase a reference book that provides more instruction to the user? But, I am hesitant to do that since I am really just evaluating if the 3D abilities in v14 is good for my company.  There seem to be a great number of BricsCAD tutorials on Youtube, but many are not English.  Is there a particular place to view a good list of BricaCAD tutorials in English?

Thanks for the help,
Joe Dunfee