error when authenticating in ubuntu software center

[Tadej Rosa]

This bug is similar to, but not the same as:
#648957 Unhandable error occured when trying to install skype4pidgin 2010-08-26 packet on Ubuntu Maverick Meerkat

In Ubuntu Software Center I wanted to install a utility that required me to add the "universe" repository to the source list. I clicked the button marked "Use This Source" and an authentication pop-up appeared. I entered the password and pressed "Authenticate", which rendered the pop-up unresponsive. The buttons still lit up when I hovered above them with a mouse, but they would not function. Nothing happened for a while, so I tried to close the window with the close button on the titlebar, which worked, but then an error message appeared. The text of the error message is the same as the one described in the previously mentioned bug. The traceback is as follows:

Traceback (most recent call last):
  File "/usr/lib/python2.6/dist-packages/aptdaemon/worker.py", line 163, in _process_transaction
    self.update_cache(**self.trans.kwargs)
  File "/usr/lib/python2.6/dist-packages/aptdaemon/worker.py", line 592, in update_cache
    self._cache.update(progress, sources_list=sources_list)
  File "/usr/lib/python2.6/dist-packages/apt/deprecation.py", line 98, in deprecated_function
    return func(*args, **kwds)
  File "/usr/lib/python2.6/dist-packages/apt/cache.py", line 343, in update
    raise LockFailedException("Failed to lock %s" % lockfile)
LockFailedException: Failed to lock /var/lib/apt/lists/lock