If you create 3D Models using SketchUp then export them some how to an STL file and load this STL file in a slicer you can get some or a lot of errors in your model.
I created a simple "cable tie holder/mount" in SketchUp 2016, saved it as an obj file, loaded it in Meshlab and exported it there to an STL file. This file I loaded into the slicing software "Slic3r".
And as you can expect I got a lot of errors.
After that, I used the STL Plugin for SketchUp to export a SketchUp project to an STL file directly, but I got the same sort and amount of error in my model after importing it to Slic3r.
The problem was, that I had a huge amount of surfaces inside the closed volume which make a faulty STL file when exported. During the design process, you will automatically create these unnecessary surfaces inside your model.
The solution is to find these surfaces and the according lines which make these surfaces. Use the wireframe view in Sketchup to find these lines and delete them until you have a clean model.
Then export it to an STL file and voila the model is no more faulty.
Here you find a post where the problem is also explained: http://forums.reprap.org
There is also a Plugin called "CleanUp³" for SketchUp which can clean your model, but in my case, it has not found all of the unnecessary lines.
If you export the SketchUp model to a *.obj file and load this in the slicing software "ReplicatorG" you won't get any errors. But this cannot be the solution because the most slicers only work fine with STL files, so you have to correct the errors in your model in every case to be able to create correct STL files!