Most likely your computer has corrupted the data in the .pkg files. There is a simple way to fix this (including loading errors)
Follow these easy steps:
1) Download a torrent client (u torrent works fine)
2) Find out what map or vehicle is having issues
3) Go to your computer/yourdrive/[either games or program files]/worldoftanks/updates
4) Find either the map package or the vehicle (by nation) and double click it to start the torrent download. once completed, proceed to step 5.
5) Open the downloaded folder, copy the file you just downloaded.
6) Open your world of tanks folder again. Go to the folder "res" and click "packages"
7) Paste your downloaded file, press yes to write over the existing one
8) Launch world of tanks
9) Enjoy