Dapper upgrade problem

[R Kimber]

I seem unable to upgrade Dapper.  Synaptic balks at x11-common.  I
tried to reinstall using apt-get and got the following output:-

Reading package lists... Done
Building dependency tree... Done
The following packages will be upgraded:
  x11-common
1 upgraded, 0 newly installed, 0 to remove and 65 not upgraded.
1 not fully installed or removed.
Need to get 0B/35.1kB of archives.
After unpacking 0B of additional disk space will be used.
Preconfiguring packages ...
(Reading database ... 110706 files and directories currently installed.)
Preparing to replace x11-common 7.0.0-0ubuntu35
(using .../x11-common_7.0.0-0ubuntu36_amd64.deb) ... /var/lib/dpkg/info/x11-common.prerm: /usr/sbin/invoke-rc.d: /bin/sh:
bad interpreter: Text file busy dpkg: warning - old pre-removal script
returned error exit status 126 dpkg - trying script from the new
package
instead ... /var/lib/dpkg/tmp.ci/prerm: /usr/sbin/invoke-rc.d: /bin/sh:
bad interpreter: Text file busy dpkg: error
processing /var/cache/apt/archives/x11-common_7.0.0-0ubuntu36_amd64.deb
(--unpack): subprocess new pre-removal script returned error exit
status
126 /var/lib/dpkg/info/x11-common.postinst: /usr/sbin/invoke-rc.d: /bin/sh:
bad interpreter: Text file busy dpkg: error while cleaning up:
subprocess post-installation script returned error exit status 126
Errors were encountered while
processing: /var/cache/apt/archives/x11-common_7.0.0-0ubuntu36_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

I'd appreciate some guidance as to how to proceed.
Thanks.
-- 
Richard Kimber
http://www.psr.keele.ac.uk/