jadesoul, this script is for 3.0. It appears it needs to be updated for 3.1. In the post above yours the creator says he’s going to try looking into it at the end of next week (which is the end of this week) 
I made a new version for 3.1, and you can get the details at the link below.
The new version is not compataible with 3.0. The visibility flags seems to have changed from 3.0, so my FlipSubVis plug-in is also broke, and will be updated shortly.
http://www.zbrushcentral.com/zbc/showthread.php?p=385571#post385571
I’ve been using this tool for a while now, it has become part of my standard workflow, I love it.
Well done GM770 
This isnt really working for me (I use 3.1). It only merges some of the subtools together (the top 2 or so in the list). Even the alt-click method (which you have to put the whole Zplugs menu into a tray to get to work, otherwise pressing alt just closes the drop down menu
) doesnt merge all my subtools, and becuase it looses the UV info, is pretty much useless.
It seems to be working for other people, so maybe it’s related to your mesh some how. Try other meshes and see what happens, or you can send me your problem mesh and I’ll take a look at it.
Problem is that it’s made for 3.1 and I got 3.0 for now no time to update 
Going to see if I can update soon !
I would have updated the link in this post, but after some time, you can’t edit your own posts. So I put that info in the latest version’s thread.
everytime i use the button make mesh…
i dont know whats goin on and my function of blurin a mask crashes too.
i dont know where to get rid of these lil bug and i got in both versions on different PCs…
Make sure you are using the proper version for your Zbrush. 3.1 users should be using the latest version 1.26b. Zbrush 3.0 users should be using version 1.24
Thanks going to test it
Fantastic script! I was hoping there would be a way to do this in ZBrush.
Keep up the great work.
Ok buddy, thanks for this plugin but I am having a problem.
I am using the right version of plugin.
When I am merging the subtools, I am not able to retain the lower subdivision levels.
I have double checked that all subtools are at same subdivision level.
Any idea how to achieve this ?
I am able to retain the levels when i use tool>geometry>insert mesh process but thats time consuming and zbrush crashes when I use about 10 subtools.
Do let me know if you can help in this.
This plug-in is designed mainly for exporting, and other apps will not support multi-res meshes. The purpose is to flatten multi-tools into 1 simple mesh. So there is basicly no way to support lower subdivisions, right now.
There is a version of this plug-in by EZ that sounds right for you. Here’s the link to it, which also has a video on how it works, so you can watch that, and see if that’s what you are looking for: http://www.highend3d.com/f/4875.html
I used it with demosoilder and imported to cinema 4d10 it works beautifully thanks for the fab plugin i love it…now to get some real work done.
Is the DL link dead?
Sebcesoir…
Download Make1Mesh plug-in - v1.26b for Zbrush3.1
http://www.mediabakers.com/files/Make1Mesh.zip
Zbrush 3.0 users should continue to use version 1.24
Spot on, thanks for this update, works great from what iv tryed so far.