I've found better luck with something like these: [ame]http://www.amazon.com/ATD-Tools-813-3-Piece-Pliers/dp/B00A7EQF8A/ref=sr_1_11?s=hi&ie=UTF8&qid=1391142498&sr=1-11&keywords=hose+pliers[/ame] The curved in tip pushes directly on the latch and fully releases it so much better than a soft squishy finger tip can ever do. With the weather-pack gasket inside the connectors are tight and take some effort to pull off.
Sometimes getting a flat screwdriver between the injector and plug bottom and twist to help push it off while using the pliers to compress the latch helps gets them off. Also you could try a very thin hook from the bottom of the latch to lift it rather than using the button to lever it up as the plastic sometimes won't lift the latch far enough even with the latch fully depressed. Without a very small hook or tiny bent screwdriver I've used a staple bent properly to do the deed before. Don't give up...they're just trying your patience!

And remember to use some connector grease on them going back together which will save you lots of grief the next time.