When I try to import a Sims 2 mesh file for Sims 3 it won't save. I have done everything correct to import the Sims 2 files according to tutorials. I'll ether get the error Model has 6 groups; original had 0 or wrong filed opened, use the "_filebase" (just a question must I import a Sims 3 object file first then overwrite?)

Max, when you're creating any object for Sims 3, whether it is a Sims 2 conversion object or not, you need to clone a Sims 3 object and then overwrite it with your new object.

The basic steps are 1. clone a Sims 3 object which is similar to the one you want to create. That is, if you want to make a chair, clone an EA chair and so on.
2. Export the MLOD and MODL from the clone package.
3. Decompile the MLOD and MODL.
4. Open the MLOD in Milkshape. Bring your new object into Milkshape with the EA object.
5. Delete the EA object.
6. Assign joints to your new object.
7. Make sure you have the same number of groups as the original clone and that they are in the same order as the EA clone's groups were.
8. Save the object over the MLOD.
9. Recompile the MLOD.
10. Repeat for the MODL.
11. Import the MLOD and MODL back into the package.
12. Test in-game.

There are details at each of these steps which are important but there are tutorials that talk about all of that. This is just the basic outline. I advise you to use EllaCharm's tutorial and do that tutorial from start to finish before moving on to the conversion project.

How can I clear the file of the existing mesh?

Here is the link:

http://www.modthesims.info/showthre...t=375349&page=1

If I were you I would throw out what you've done as far as the .package goes and just start over on the conversion project after you've done the tutorial. I have no idea what kind of errors you've made since it seems you started out without any background at all. The MLOD, at least, is broken for sure if it's giving you that 0 groups error. This error shows up if you strip the joint off the object, ignore the error message having no joint gets you, and recompile with no joint.

The best thing is to start from scratch once you have a better idea of what you're doing

The Sims 2 file is not in MODL or MLOD file jet I'm reading through the tutorial it tuns out I already downloaded it but haven't finished reading it jet. Only thing i need to know still is how to see the groups in S3OC

Are you working with TSRW?
Then,

-clone a similar sims 3 object
-Export the mesh in the mesh tab
-Import that mesh in Milshape with TSRW's WSO plugin
-Import your custom sims 2 mesh with Wes H his unimesh plugin
-Rename the sims 2 mesh same as the sims 3 group, then delete the original sims 3 mesh
-Export with the WSO plugin
_import in TSRW in the meshtab.

As far as I know, you don't see the actual mesh groups in S3OC. This program is just used to clone an existing game object, so you can replace it with your own. I'm not even sure if you can see the see the groups in S3PE. Usually the mesh groups are important in Milkshape, where you can see them in the groups tab when you open your MLOD/MODL. And the ObjectTool will also give you a listing of the groups of your MLOD/MODL file.

And you clear the file of the existing mesh by exporting the meshfiles in S3PE, decompiling them in ObjectTool, opening them in Milkshape and replacing them with your own. Then you need to save that mesh in the existing MLOD/MODL files (the ones you exported and decompiled), then recompile them (also in ObjectTool) and re-import them into the package file in S3PE.