Then on the opposite side there are a bunch of naked edges around this filleted area:



It looks like it's these fillets that caused your object to become not solid so that's where the trouble started probably.

See for example these fillets here:



Even though that really looks like 2 fillets with a thin surface between them, that's not what it is - it's actually just 2 fillets with no surface between them, the fillets overshoot past each other by a little bit. So it looks like you used a fillet radius that was just slightly too large to fit in the available space. The fillets were still generated but their ends are not attached to anything.

It would probably be easiest to erase this front protrusion and build it again with a smaller fillet radius. To erase it you can delete all the faces making up that protrusion which will leave a hole, then you can select the edges around the hole and use delete on those too doing an "untrim" (it's covered in that object repair tutorial linked to earlier, also here: http://moi3d.com/forum/index.php?webtag=MOI&msg=444.4) .

That will remove the protrusion so you'll need to rebuild that area:




But now with these steps done your object is back to being a solid and booleans on it should be back to behaving normally again.

I've attached the solid object 3DM file here as repaired_object_3dm.zip .

Hope this helps explain what happened and how it's fixable.

- Michael