You can install Media Encoder and other Creative Cloud apps on up to two computers. If you want to install it on a third computer, you'll need to deactivate it on one of your previous machines. Learn more about activating and deactivating Creative Cloud apps.
There could be a problem with the way the footage was encoded. When Media Encoder encounters frames that cannot be decoded, it inserts red frames in their place. Learn more about fixing red frames in your Premiere Pro export.