There are errors solid inspector cannot fix, but TIG’s solid solver found a number of coplanar edges and after correction the skp is now reporting solid. IHMO it is great to have a program to flag errors, but with the number of edges asking folks to do that manually seems questionable in my mind especially with the number of programs that will solve on batch basis. On top of that then to properly 3d print there usually wants be added an internal shell so it deleting internal geo is just a fraction of the solution.
Hmac1AA.skp (256.0 KB) ere is the solid skp file but suggest you run it throught the free version of Netfabb as noted above to just get confirmation of its " solidness".
Here is the stl file mac1AA.stl (911.0 KB)
Depending on the print technology you are using some other mods may be necessary see the materialize info in the 3d ware house to help you.
I just found a free program called meshmixer that appears very powerful to help you get model in shape to print. It is not a plugin but program.