Does any of these applies to you?
"Exploit failed, please try again." Error: You'll be seeing this a lot. Just hold down the power button on your WiiU console until it shuts off completely, then start it back up.
Crash after running exploit 2 times and returning to Home Menu: There was a Fatal Error and the system halted. Either you are trying to install a non-public or unsafe Title or your SD card is incompatible, not formatted correctly, or doesn't have the appropriate files in the install folder. You may also be trying to install an existing or older version of an existing Title, which will not work.
Black Screen/No Error/Artifacts/Crashes on Browser Mii: There seems to be an issue with the current Webkit exploits if you do a major system update or choose the option to do a full Browser Data Reset (or have just never used the Browser before). To resolve this, follow these steps:
1. Open Multiple tabs with heavy content sites (Youtube, Facebook, etc.)
2. Press Home then return to the main dashboard
3. Power off your WiiU properly from the controller
4. Turn it back on and test the WUP Installer again
** This may also be an issue with your SD card, try launching the first stage without an SD card inserted to see if it works.
If you do not exit the browser properly then reboot the console and just try to launch the WUP Installer, the Browser cache file doesn't seem to write out properly and you'll just get a black screen again. You may need to do this several times, it can take up to 2 hours, but once the exploit starts working, however, you will typically never have to do it again.