only thing I can think to try is to create that folder
/App_Themes/userpersonal1/
and copy the theme.skin file from the skin folder into that folder
maybe that would get it past the error
if you can access the database, then look in the mp_Sites table, set AllowUserSkins to 0
and try changing to a different skin in the Skin filed to the name of a newer skin. You can copy the newer skins from /Data/skins into /Data/Sites/1/skins