Corrected missuse of Exception instead of Error.

Change-Id: I890ba47c7739e07f6db8ecdbdcca3ff306acf292
Reviewed-on: http://review.couchbase.org/26460
Tested-by: Brett Lawson <brett19@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>