After git merge: "Trying to write ref refs/heads/master with nonexistant object"

gistfile1.txt

remote: Counting objects: 45900, done.
remote: Compressing objects: 100% (14129/14129), done.
remote: Total 45900 (delta 30836), reused 44791 (delta 30042)
Receiving objects: 100% (45900/45900), 52.81 MiB | 18.27 MiB/s, done.
Resolving deltas: 100% (30836/30836), done.
error: refs/remotes/origin/master does not point to a valid object!
error: Trying to write ref refs/heads/master with nonexistant object 38eca7173be01a36ef03ebcf75732eba32e4038d
fatal: Cannot update the ref 'HEAD'.


But the object exists in the git repository:

ls -l ./objects/38/eca7173be01a36ef03ebcf75732eba32e4038d
-r--r----- 1 gitolite gitolite 191 Sep 20 15:45 ./objects/38/eca7173be01a36ef03ebcf75732eba32e4038d


The object seems OK on the server:

gitolite@code:~/repositories/zhdk-typo3.git$ git cat-file -p 38eca7173be01a36ef03ebcf75732eba32e4038d
tree 8edd1a6a3d9b309402edcde6f49526400a0ac487                                                                                                              
parent 846c4b22ea89475cb70ca0bfe1e67b84f4118c0c                                                                                                            
author Ramón Cahenzli <rca@psy-q.ch> 1348148745 +0200                                                                                                      
committer Ramón Cahenzli <rca@psy-q.ch> 1348148745 +0200                                                                                                   
                                                                                                                                                           
ApiGen: No need to check for new versions.       




While cloning, the directory on the client looks like this:

/tmp/blah/.git
/tmp/blah/.git/objects
/tmp/blah/.git/objects/pack
/tmp/blah/.git/objects/pack/tmp_pack_oju5Af
/tmp/blah/.git/objects/pack/tmp_idx_hk216m
/tmp/blah/.git/objects/info
/tmp/blah/.git/config
/tmp/blah/.git/refs
/tmp/blah/.git/refs/heads
/tmp/blah/.git/refs/tags
/tmp/blah/.git/info
/tmp/blah/.git/info/exclude
/tmp/blah/.git/description
/tmp/blah/.git/HEAD
/tmp/blah/.git/branches
/tmp/blah/.git/hooks
/tmp/blah/.git/hooks/commit-msg.sample
/tmp/blah/.git/hooks/prepare-commit-msg.sample
/tmp/blah/.git/hooks/post-update.sample
/tmp/blah/.git/hooks/post-commit.sample
/tmp/blah/.git/hooks/pre-applypatch.sample
/tmp/blah/.git/hooks/pre-rebase.sample
/tmp/blah/.git/hooks/post-receive.sample
/tmp/blah/.git/hooks/pre-commit.sample
/tmp/blah/.git/hooks/applypatch-msg.sample
/tmp/blah/.git/hooks/update.sample


The git version on the server is 1.7.10.4, the client has 1.7.2.5, both on Debian.