Can't update translations with gettext:find_theme

[garethrees]

gareth: ~/Code/alaveteli-themes/asktheeu-theme (master $=)
$ git status                                              
On branch master                                          
Your branch is up-to-date with 'origin/master'.           
nothing to commit, working directory clean

vagrant@vagrant-ubuntu-precise-64: ~/alaveteli
$ bin/rake gettext:find_theme THEME=asktheeu-theme
/home/vagrant/alaveteli/lib/themes/asktheeu-theme/locale-theme/app.pot /home/vagrant/alaveteli/lib/themes/asktheeu-the
me/locale-theme/de/app.po msgmerge: input file doesn't contain a header entry with a charset specification
Failed to merge with /home/vagrant/alaveteli/lib/themes/asktheeu-theme/locale-theme/de/app.po
New .pot was copied to tmp.pot~
rake aborted!
Check these po/pot-files. It may have syntax errors or something wrong.

Tasks: TOP => gettext:find_theme
(See full trace by running task with --trace)