Similar issue while upgrading Ubuntu Mate from 16.04 to 18.04.
(Reading database ... 324225 files and directories currently installed.)
Preparing to unpack .../libidn11_1.33-2.1ubuntu1_amd64.deb ...
dpkg: error processing archive /var/cache/apt/archives/libidn11_1.33-2.1ubuntu1_amd64.deb (--unpack):
triggers ci file contains unknown directive syntax
Errors were encountered while processing:
/var/cache/apt/archives/libidn11_1.33-2.1ubuntu1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
A package failed to install. Trying to recover:
Similar issue while upgrading Ubuntu Mate from 16.04 to 18.04.
(Reading database ... 324225 files and directories currently installed.) 1.33-2. 1ubuntu1_ amd64.deb ... apt/archives/ libidn11_ 1.33-2. 1ubuntu1_ amd64.deb (--unpack): apt/archives/ libidn11_ 1.33-2. 1ubuntu1_ amd64.deb
Preparing to unpack .../libidn11_
dpkg: error processing archive /var/cache/
triggers ci file contains unknown directive syntax
Errors were encountered while processing:
/var/cache/
E: Sub-process /usr/bin/dpkg returned an error code (1)
A package failed to install. Trying to recover: