Output errors come in a variety of types. The two most common are "Output file wrong size" and "File size error - no more bytes to read."
What is happening is the WildTangent Games App is trying to download a game, but pieces of that download are being blocked by the security software installed on the computer. The computer is expecting the game file to be a certain size, and it isn't.
To fix this error, you just need to configure the security software settings. We have a Security Software Article that will help you with that.
Once you've done that, reboot the computer and try your download again!