Debian 4.0 installation problems (libpam-plesk_8.3.0...)

[sts_fin]

The swsoft_installer_v3.3.0_build080116.12_os_Debian_4.0_i386 cant finnish install

gives this error:

Unpacking libpam-plesk (from .../libpam-plesk_8.3.0-debian4.0.build83071218.18_i386.deb) ...
Errors were encountered while processing:
/var/cache/apt/archives/psa-courier-imap_3.0.8-debian4.0.build83071218.18_i386.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

Im running debian 4.0
Linux 2.6.18-5-686 #1 SMP Mon Dec 24 16:41:07 UTC 2007 i686 GNU/Linux


Is there a workaround? can anyone help?

i have been strugling with this for three days...