The pressure in my column in position 2 gets very high and shuts down the pump. Following the pathway all the way to the needle seat there is no issue, when disconnected from any of the pathways beyond the column the pressure is normal in my column. I have another column for a different drug in position 4 with no issues at all. What could be the problem? It can't be the needle seat if one pathway works and another doesn't. Any ideas?