Bug#621836: exim4: Could not perform immediate configuration

[Grant McLean <grant@catalyst.net.nz>]

I have this same error.  I have a server with ssmtp installed and I wish
to replace it with exim.  So I tried this command:

# apt-get --purge install exim4-daemon-light ssmtp-
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following extra packages will be installed:
  exim4-base
Suggested packages:
  eximon4 exim4-doc-html exim4-doc-info spf-tools-perl swaks
The following packages will be REMOVED:
  ssmtp*
The following NEW packages will be installed:
  exim4-base exim4-config exim4-daemon-light
0 upgraded, 3 newly installed, 1 to remove and 0 not upgraded.
Need to get 0 B/2,079 kB of archives.
After this operation, 4,166 kB of additional disk space will be used.
Do you want to continue [Y/n]? y
E: Could not perform immediate configuration on 'exim4-daemon-light'. Please see man 5 apt.conf under APT::Immediate-Configure for details. (2)
# 

Adding the -o APT::Immediate-Configure=0 gives the same result.

Also the same result with the simpler:

  apt-get -o APT::Immediate-Configure=0 install exim4

No doubt I could work around this by purging ssmtp first but that will
result in the removal of a bunch of packages that depend on an MTA and
I'd prefer not to do that.

Are there any commands you'd like me to try in order to help debug this
situation?

Regards
Grant