This is currently a known bug with the pool's interaction with CG/SGMiner. Terk hasn't been able to smash this yet.... good news is that it's just a visual issue on CGMiner and SGMiner and does not really affect your work/earnings. Check the site for the real reject rate or estimate it from the per GPU rate displayed in CGMiner. Definitely don't go by the CGWatcher or CGRemote numbers, because they'll be based on the bogus reject rate shown in CGMiner.
More info: https://bitcointalksearch.org/topic/m.5538219
What reject rate does the Clevermining site show for you?