How to fix broken repository information?
The first step is to cut out the "middle-man" tools and work with commands that are invoked on your behalf:
sudo apt-get check && sudo apt-get update
# you may need to repeat the update if it complains
sudo apt-get upgrade
Any errors generated by these commands would be most informative when appended to your original question. If the check fails, do as it instructs or stop and post your result.