Thank You, Dave and Marcus! The new version got approved for 3D printing. It must have been the blue faces and/or soft edges. Good to know.

I've tried sending this design to get 3D printed, but had it returned to me due to unclosed contours. I've used the Solid Inspector plugin, but it didn't show me any errors. And entity info tells me that this object has a volume. Can someone tell me what the problem is? Also, do blue faces on an object cause it to be not a solid? Do I have to reverse those faces?

probe1_scaled.skp