whoisgregg - 9:05 pm on Jun 4, 2012 (gmt 0)

Is the actual column name fulltext? If so, take a look at the reserved words list [dev.mysql.com] and try to avoid those in the future. Meanwhile, use backticks around the column name and see if that helps:

UPDATE `j25_content` SET `fulltext` = CONCAT(`fulltext`,'<p>newtext</p>');