when you first create your mocs, are you selecting one of them as the main pic? if not then it will always create the moc without a preview/main picture.
similarly, if you have chosen on, then edit and add new pictures with the uploader, you MUST remember to select "another" option or it will replace the main picture when it adds the new pictures.
Also the uploader always adds new pictures to the top of the page, when you move them about you must remember to not delete any HTML code or nothing will be visible.
Finally, try saving your mocs without adding text, then going back in and editing them later, sometimes edits get "forgotten" by your computer if you have been working on them a long time before saving. Permalink