Cannot locally 'sync-all get'

[Daniel Fischer]

Like so often, ./sync-all pull failed today in my local clones, first with 
"... not on a branch", after sync-all checkout master, with "fatal: Reference 
... not a tree". (Aside, that nonsense didn't happen before the introduction 
of submodules.)

The usual remedy is

rm -rf ./clone
git clone ./ghc ./clone
cd clone
./sync-all get

but today it failed with

> Klone nach 'libraries/xhtml'...
> Fertig.
> Unterprojekt-Pfad: 'libraries/xhtml':
> 'fb9e0bbb69e15873682a9f25d39652099a3ccac1' ausgecheckt fatal: Projektarchiv
> '/home/dafis/GHC/./haddock.git' existiert nicht. Klonen von
> '/home/dafis/GHC/./haddock.git' in Unterprojekt-Pfad 'utils/haddock'
> fehlgeschlagen git failed: 256 at ./sync-all line 123.

Any idea what's up?

Cheers,
Daniel