I ACTUALLY just started working with mesh, and yes I had that issue all day. The reason is because with those 3d models, need you to create the physics model . Basically you have to create a physics shape for the models since that determines how avatars interact with the object. I got this from
http://wiki.secondlife.com/wiki/Mesh/Exporting_a_mesh_from_3ds_Max
Creating Your Models
For basic information on how to use 3ds Max, see the Autodesk 3ds Max Tutorials page, the excellent built in help, and the many third party books, video tutorials, and training courses. This section only covers specifics to creating a model for upload to Second Life.
You can use any of the modeling tools while working on your item, but in the final form it should be saved as an Editable Poly, with Reset Transforms applied, and the stack collapsed.Each object in the 3ds Max scene will import as a separate object in Second Life. If you want your model to appear as a single object once imported, use the Attach function in 3ds Max so that it appears as a single item in the object list.You can use up to 8 Material IDs. These will import as Faces in Second Life, which can be individually textured. You need to create a UV mapping for your model which defines what part of the texture will go on which polygons of the model. Fewer Material IDs/Textures are more efficient, and you can combine polygon groups from different parts of your model onto a single map. If you use more than one ID, then set up a single Multi/SubObject material with as many sub-materials as you need, and apply that to the whole object.You can define up to 4 Level of Detail (LOD) versions of your model for viewing at different distances. Using simpler versions for far away items saves server and PC workload, and you are rewarded for that with a lower Prim Equivalent use of parcel prim allowance. Each LOD version is saved as a separate Collada .dae file and selected in the upload window. Additionally you can define a Physics Shape which controls how the object collides with the terrain, other objects, and avatars. Complex collision physics is a heavy load on the server, so the Physics shape should be as simple as possible. It is invisible once imported to Second Life. All LODs and the Physics shape will share the same Bounding Box. This is an imaginary box aligned with the X, Y, and Z axes just large enough to contain the model. So keep that in mind when creating the various versions, so they line up properly. The LOD versions need to use the same number of Material IDs, but the layout can be different per version.If you want to make an animated attachment (one that bends and follows the underlying avatar movements), then apply the Skin modifier last in the Command Panel > Modify tab. The set of bones must be identical in name and structure to the one used in Second Life. For rigid attachments or non-attached items to be used on a land parcel, you can skip this step.Second Life is a real-time environment, and typical Viewers have a few tens of milliseconds to render the entire scene (1 second divided by the frames per second speed). So mesh items should use the least number of triangles and vertexes as possible while looking the way you want it. High detail models used for offline animation and rendering are not suitable. Smoothing varies the shading across the model, giving the impression of a curved surface without a lot of triangles. When different smoothing groups meet at an edge, or when smoothing is not used, the shading will change abruptly at the edge, and give the impression of flat sides with a sharp corner. You can display current polygon, triangle, and vertex count within the 3ds Max viewport to keep track while you work.