Cannot install or uninstall packages

Lately i installed sun java in my ubuntu 11.04, after that when ever i try to install or uninstall a package from software center
or synaptic the following message comes :

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/aptdaemon/worker.py", line 961, in simulate
    trans.unauthenticated = self._simulate_helper(trans)
  File "/usr/lib/python2.7/dist-packages/aptdaemon/worker.py", line 1085, in _simulate_helper
    return depends, self._cache.required_download, \
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 226, in required_download
    pm.get_archives(fetcher, self._list, self._records)
SystemError: E:I wasn't able to locate file for the sun-java6-bin package. This might mean you need to manually fix this package.

also in the terminal if i try the following message comes :

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  esound-common libesd0 libaudiofile0
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
  sun-java6-bin sun-java6-jre
Suggested packages:
  sun-java6-plugin ia32-sun-java6-plugin sun-java6-fonts ttf-kochi-gothic
  ttf-sazanami-gothic ttf-kochi-mincho ttf-sazanami-mincho ttf-arphic-uming
Recommended packages:
  gsfonts-x11
The following packages will be REMOVED:
  firefox firefox-globalmenu
The following packages will be upgraded:
  sun-java6-bin sun-java6-jre
2 upgraded, 0 newly installed, 2 to remove and 0 not upgraded.
2 not fully installed or removed.
E: Could not get lock /var/cache/apt/archives/lock - open (11: Resource temporarily unavailable)
E: Unable to lock directory /var/cache/apt/archives/

please help me...!