ajorge, the skin page does not show any thumbnail means that it can't find any .ascx file in the skin's folder. You should check the zip file of your skin package and see if the files in your skin (and container if you have one in the same place) have the "path" attribute set to "/skins". If so, it means that you zipped the skin in a wrong way. You might have zipped the whole skin folder instead of  its files only. In this case, your skin structure will look like this : "/Portals/[PortalNo.]/Skins/[SkinName]/Skins/[SkinFiles]". To fix it, simply repackage the skin by following this step : Zip the skin files only (not the skin folder!) to Skins.zip , zip the container files to Containers.zip and finally zip these 2 to [YourSkinName].zip . If you have only the skin (no container), you just have to zip the skin files to [YourSkinName].zip and upload it to the portal.

Hope I assume right

Duc