The preinst scripts in both the x2goserver and x2goprint debs add sudoers entries. When adding the packages to an existing installation this is adequate (although it may violate a Debian packaging policy somewhere).
If the packages are installed during a Debian/Ubuntu installation using kickstart and/or preseeding it causes a conflict. The problem is that the entry "%admin ALL=(ALL) ALL" is added after the installation/post-script stage. If x2goserver or x2goprint is installed, their NOPASSWD entries are already in sudoers and the %admin entry overrides them since the file is processed from top to bottom. This causes x2go connections to fail with "sudo: pam_unix(sudo:auth): conversation failed" and "sudo: pam_unix(sudo:auth): auth could not identify password for [user]" errors in auth.log (an infinite number as it really doesn't want to give up until I kill x2gostartagent).
Preseed options/templates need to be added to these debs so that the sudoers entries can be skipped via preseed/debconf and added later by a late_command script or manually after installation.