Toilets, Sinks, Showers, Tubs and Disposals - PEX to Copper bathroom Sink Connector leaking

I am coming to the end of a project to run PEX throughout my house, but I am running into a problem with the sink bathrooms.

Current connection:
http://www.mcraignet.com/Images/PlumbingSink.jpg

The copper connectors past the valve are leaking in half of my connections. I've tried Teflon tape, but this does not resolve the issue. In one of the two leaky connections, it is actually spraying above the copper/brass nut.

How do I use these connectors without cutting the copper tubing and therefore cutting the lip that would hold it on?

PEX Unused Connector:
http://www.mcraignet.com/Images/PlumbingConn1.jpg
http://www.mcraignet.com/Images/PlumbingConn2.jpg

Thanks,
Mike

Mike:

It would appear to my eyes (questionable eyesight) - that you have compression fittings for your application. Yet you mention a "lip" on your tubing, which sounds like "flare fittings". The two are not interchangeable.

If you have compression fittings, you will have a small ferrule that slips over your copper tubing and a compression nut that "compresses" the ferrule when tightened to create a watertight seal. Towards that end......... (if that's what you've got)..... cut your tubing clean and remove burrs/shards (no lips). Use some emery cloth to clean the tubing to a dull shine. Put the nut on first, followed by the compression ferrule and insert into your valve fitting, tightening only enough to keep it from blowing off when you turn your water on. Once you turn on the water, tighten the nut slowly, 1/4 turn at a time, until the water stops leaking from the joint. Hopefully, that will get you where you want to be.

That was the problem sinks are no longer leaking, thanks Thezster.