This might not be very reassuring but after I started my first Pirate I only played briefly and went back to W101. When I returned after about a year and a half I found that I had a whole stack of "gifts" that I'd gotten from various fan-site give-aways which gave gifts for W101 and P101. Anyway, when I tried redeeming those gifts I got the same message you did... "The item failed to redeem". This went on for a day or so then all of a sudden - boom - I tried it again and it worked. I have no idea what kept them from redeeming the first few times I tried it but for whatever reason the problem eventually resolved itself.
Don't open your backpack or work with your crew or feed your pets or ANYTHING until you've tried to redeem the gift(s) you're wanting on that pirate. When you switch out characters, actually get into the game a second or two before changing back to the other character. When all else fails, log out completely and log in again, then call up that pirate and grab the goodies.
When you first enter the game, Immediately REDEEM your gifts (don't do ANYTHING else). If this doesn't work, press 'b' to open your Backpack and make sure you have enough room in it. For most items you will just need one space per item since any gift that you redeem goes into the Backpack. The exceptions are Bundles and other multiple gifts which can take up to seven places in your Backpack.
If you didn't have enough room in your Backpack and had to clear some space for the items, go to the Pirate Selection Screen, choose a different Pirate, now click on the Pirate you want to have the item, and click Play. Immediately REDEEM your gifts. That has worked for me in the past.
If you only have one Pirate, you may have to exit the game and restart it.
The reason you might not have enough room in your Backpack is because you were a member and aren't now. Members get a Backpack with room for 120 items and non-Members only get room for 80 items.