If these 4 lines are really the only content of your /etc/apt/preferences file, you might safely remove it.
There is the crucial information about what to pin missing as stated in the error message. That line would be some 'package: PutYourPinnedPackageHere' before the lines that are still there.
May be you wanted to pin some package and just did an incomplete copy'n'paste???
Do you have firefox installed? If so the repo entry with chinook is what they are using .