Software centre crashes when adding source

[Reece Dev]

There seems to be a programming error in aptdaemon, the software that allows you to install/remove software and to perform other package management related tasks. Please report this error at http://launchpad.net/aptdaemon/+filebug and retry.

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