Please attach here your /etc/apt/sources.list and do at terminal:
ps xua |grep update-manager to see if it's running. You have apt-get locked so that's why you can't use it.
Please attach here your /etc/apt/ sources. list and do at terminal:
ps xua |grep update-manager to see if it's running. You have apt-get locked so that's why you can't use it.