There are many reasons for this type of failure. Decks are probably the toughest exterior surface to maintain.
Though most mills have gotten away from the practice, some still ship lumber with whats called a Mill Glaze. This is a temporary finish that keeps the wood looking new even though it may be exposed to the weather for several months. The glazing is easy enough to remove, a washing with a power washer is usually sufficient.
A couple of questions here, did you wash the deck first? What part of the country do you live in and if your in the north, do you have enough of the season left to redo it or would it be better to wait for the spring?
Some other reasons for failure would be too much moisture in the wood, any thing over 15% would keep your finish from adhering. Direct sunlight, if your deck sits in the sun for the majority of the day, your finish won't last.
I would be the last to say that Cuprinol is a lousy product, I've never used it. All the decks I finish recieve Super Deck (I think this stuff is made by Duck's Back, Chico, California) The only draw back to this stuff is that it doesn't come in a clear finish. The lightest one (Natural) is clear but has an amber color to it.
Even with the best of products, though, your deck will be a maintainance issue. You'll need to reseal it every 2 to 3 years.
Others, here may have differing ideas as to what to do now, but I'd reccomend that your get a power washer, one with ample pressure (3000psi or greater) and give your deck a good washing, followed up with a wood brightener such as Oxillic acid or even chlorox bleach mixed with water and applied liberaly and thoroughly rinsed. If you've never used a washer before, you may consider having someone with expirence do it. If your into adventure, and want to try it your self, practice first on a piece of cheap plywood.
The strokes with a washer should be as follows: Start with the wand pointing away from the surface your going to wash and pull the trigger, then sweep the wand down to the surface and about 4 to 6 inches away and sweep the wand the length of your reach or walk wit the wand. When you've reached the length of the stroke, sweep the wand up and then let go of the trigger. This will avoid blast lines on your wood.
Allow your deck to dry for several days and then refinish with the Super Deck. A word of advice here would be to get a sample of wood and apply a coat of Super Deck to it so you know what it will look like before you apply it to your whole deck.