If you have blocks that have entities inside that are on a layer you want to purge, there is an alternative way of cleaning it out. It's a favorite trick of mine I dig up every time nothing else works.
A dxf file is a text file, and a text search and replace will work. Say you have a layer "A-Glass-Wall". You can search for "A-Glass-Wall" and replace with 0.
A dxf file for a good sized .dwg will have several million lines, so you can't use an in-memory editor like notepad. I have Unix utilities, so I use SED. But, if you don't have a streaming editor, you can write a small program to open the dxf file and loop through it replacing as you go.
If you are a real dxf expert, there are other editing tricks -- like replacing z coordinates with 0. As always, be careful. A global search and replace could create a monster that crashes when you try to load it. Make sure you save everything before you start.