maybe there is stuff inside $news_html that looks like sql? the culpret might be the first single qupte, which would look like the ending of your inserted variable
try reformatting yout $new_html string to be sql_safe, this is dependant on your database but just replacing all your ' with '' should be sufficient for mysql, also if it won't wreck your code to remove all ; characters i'd do that just to be safe, since ; could accidentally end the sql statement too soon
[man]str_replace[/man]( "'", "''", $news_html );
[edit]
mahers example will work also, it wasn't up when i hit reply