Error message (12) – WP first opens – How to remove?

Can some kind person please advise what I can do to fix this error which is repeated about 12 times as WP opens
Quote
Warning: preg_match() [function.preg-match]: Compilation failed: nothing to repeat at offset 1 in /home/content/73/6823373/html/discountvoucherclub-com/wp-includes/classes.php on line 210
Unquote
as you can tell the site is discountvoucherclub.com
we are unsure when or how this error first occurred (or what to do to avoid future occurrances)
Have installed another theme – no change – error still showed
then
re-installed this original theme – error still displays to PUBLIC
and
in the DASHBOARD – the error is the same but with 2 additional lines
quote
Warning: Cannot modify header information - headers already sent by (output started at /home/content/73/6823373/html/discountvoucherclub-com/wp-includes/classes.php:210) in /home/content/73/6823373/html/discountvoucherclub-com/wp-includes/functions.php on line 830
unquote
.
I am then NOT able to get any access (via DASHBOARD) to see if POSTS and PAGES data is still held in database etc
.
Your advice and guidance much appreciated.
Mark