Even if your SKP model is perfectly formed and a 'solid', there can still be limitations with the 3d-printer itself.
Sometimes fine details or thin parts cannot be manufactured.
Because you can model it doesn't mean you can 3d-print it.
Such limitations vary with the 3d-printer-type and the material being used.
The printing-firm should give guidance on the minimum [and maximum] sizes - like indentations, surface protrusions, thin walls, slim post/beam sections etc... these are often often ~1mm and 3mm respectively... but find out...
If in doubt ask...
Your SKP model needs to be setup to be printable - they want you to succeed - so get it right before submission...