When previewing an article, there is the usual "edit"-link on the article that is previewed. However clicking it provikes an error since the article has not been saved yet. I think it would be a nice thing to remove it on the preview-page.
Not fully tested, but try this:
In lib-common.php, function COM_article(), add $mode and $LANG24 to the list of the global variables (first statement in that function). Then, a bit further down, change
if( SEC_hasAccess( $A['owner_id'], ...
to
if(( $mode != edit ) && ( $mode != $LANG24[9] ) && SEC_hasAccess( $A['owner_id'],...
bye, Dirk