Found in proxy log :

7783:20140129:152629.369 [Z3005] query failed: [0] Expression tree is too large (maximum depth 1000) [delete from items where (itemid between 48907 and 48928 or itemid between 48930 and 48944 or itemid between 48955

20902:20140129:090019.179 failed to update local proxy configuration copy: database error