Solid Group looking poor from repair service

Hello all
Can someone explain why the following happened
Made a number of entities each a solid group as shown on the entity info dialog box
Joined them all together using outer shell now showing one Solid Group
Sent model stl, to repair service just to see what it would look like
Came back as an stl, imported it into skp
What a mess it came back as
Any explanation

Without seeing the model or the very least an image, how could anyone answer.

An image or SKP would be very helpful!

A group containing just geometry can report as a ‘solid’… BUT not be useful in 3d-printing.
This is because to decide if an object is a ‘manifold solid’ SketchUp determines if every edge has exactly two faces.
But if some faces intersect each other, so that a part of one volume penetrates into another volume it can’t be printed.
To fix it you need to intersect all of the group’s geometry.
At that point it will no longer be seen as a ‘solid’ - some edges will now have more than two faces.
You then need to erase internal partitions etc until is is again a solid…
There are tools to help you do this try my SolidSolver [ SketchUp Plugins | PluginStore | SketchUcation ], or thomthom’s SolkidInspector2 [ SketchUp Plugins | PluginStore | SketchUcation + requires TT_Lib SketchUp Plugins | PluginStore | SketchUcation ]

Thanks Tig you have solved my solid group problem. Now on to my next problem hahah