UPDATE:

Nintendo tech service says they need to check my Wii U to see why I can't access its system memory. However, it turns out I can download new games and files straight into a external hard drive and run it from there. 

However, will I be able to run the future Smash Bros DLC on an external hard drive if I have the smash bro game file and save data on the Wii U's system memory?

Solved: Turns out the DLC will try to download where the game file is stored (system memory) even if the system has no room and the external HD does. 

Original Problem:

Ever since I downloaded Donkey Kong Country Tropical Freeze into my Wii U's internal hard drive, the sytem is struggling to open its system memory. 

Basically I can go to settings --> data management --> move/delete/copy data ---> system memory 

After selecting system memory, the Wii U gives me a preparing window that never seems to go away. I tried letting it run for an hour and it still wouldn't load! 

This is a big problem because i have less than 900 MB left and I want to test out the new dlc for Smash Bros and Mario Kart ASAP!!  Anyone know why this is happening and who I can contact for support? I tried to go on Nintendo tech support forum but logging in to my club nintendo account keeps giving me an error web page! 

"...the sytem is struggling to open Data Management..."

You can enter storage option in Configuration menu, but you can't see any storage device to acess data management, right?

Does the console leave you any message?

I can see the storage device actually. I messed up earlier saying it can't access data management. It can open this option but when I get to the screen that lets me click system memory and click it, the Wii U tell me its preparing to open system memory but it never opens it. I let it ran for a whole hour before and it still won't open.

Basically I can go to settings --> data management --> move/delete/copy data ---> system memory 

After selecting system memory, the Wii U gives me a preparing window that never seems to go away.

What if you turn off the console and plug off the HDD to see what happens? If you can access to system memory after this, then I think there's an issue with the hard drive. You should try to access again to the system memory with the HDD plugged, though.

I don't have a HDD with me that I can use. I have connected a 1 GB USB to see what happens but the result was the same.

Oh, sorry! I got it. Since you downloaded Tropical Freeze I thought you needed to use an HDD, but it wasn't the case.

The solution would simply to reinstall the game, but since you can't access to the data management, I have no clue :/

Yeah I definitely stumbled upon a weird tech issue. Thanks for the help, though!

AFIK WiiU doesn't have internal HDD.

So if I got that right, your problem it's with the System Memory and not the HDD?

I had a problem with an old HDD that was kind of mess up, I could open the system memory and I could move small games (like indies, VC, etc) but when trying to move big games from the System Memory to the HDD (and viceversa) I always got an error and had to restart the system. Also, the games that were on the HDD crashed during loading screens. I just changed the HDD to a new one and haven't had any problems yet, did have to download all games that were on the HDD again though.

Not sure if this will help.

As a general question, can you play games that are on the internal Wii U's memory without problems?

The Club Nintendo page has been down for me ever since they announced the rewards, but today I was finally able to log in and claim the game, so maybe you could try the forums again. If your problem it's with the internal Wii U's memory then you should contact Nintendo asap.

Oddly enough it kind of sounds like part of your SSD in the Wii U might be corrupted or the symlink might be corrupted. If you are able to format the HD I would likely consider doing that, but there are risks to that as well.
I would call Nintendo and find out what they say. Likely have to send it in to get it sorted.