For Viewer 2,
I follow this when I'm a cloud that won't manifest if Advanced>Rebake Textures (Ctrl+Alt+R) doesn't work:
Go to
Menu>Advanced>Show Debug Settings>RenderUnloadedAvatar> then Select True and Close the window.
If you don't show an "Advanced" menu item Ctrl+Alt+D will bring it up
If this doesn't work, you need to clear your cache and if that doesn't work, uninstall and reinstall SL.