WatchGuard proxy error - header-line too large

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http://serverfault.com – When trying to access new threads on a forum, I am receiving the error below. It seems like post count on the forum may have reached a point that it is generating a HTTP response header that is too large. Which setting in the WatchGuard HTTP proxy will allow me to fix this issue? Response denied by WatchGuard HTTP proxy. Reason: header-line too large line='Set-Cookie: hfthread_lastview=1f2b28063f6e3b509884091e30300fdf83ef1b4aa-174-%7Bi-1678510_i-1331573202_i-1679284_i-1331575394_i-1679388_i-1331579857_i-1678606_i-1332367647_i-1679180_i-1331577384_i-1678922_i-1331582026_i-1676987_i (HowTos)