apt-get issue

Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following packages will be REMOVED:
  at
The following packages will be upgraded:
  apache2 apache2-mpm-prefork apache2-utils apache2.2-common libkrb53 libpq5 linux-image-2.6.26-2-amd64
7 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
5 not fully installed or removed.
Need to get 0B/24.9MB of archives.
After this operation, 2798kB of additional disk space will be used.
Do you want to continue [Y/n]? y
Preconfiguring packages ...
(Reading database ... 41401 files and directories currently installed.)
Removing at ...
dpkg: error processing at (--remove):
 cannot remove `/usr/sbin/atd': Permission denied
Processing triggers for man-db ...
Errors were encountered while processing:
 at
E: Sub-process /usr/bin/dpkg returned an error code (1)