Maybe the following extracts from two logfiles can help to pinpoint the cause.
I was allready suspecting the SRVR_THRD because it was often the last entry in one of the logs.
On this laptop I am running 2 main and 1 dev client (different tracks allways)
As you can see this time both logfiles had the same last function called.
On a side note: the hang happened at 0:04 according to the timestamps on the autosaved files, that was just after a puzzle closed.

Main:

Playing sound: 4
SRVR_THRD sending: 308854 992848 group_score
SRVR_THRD error: Error: database returned invalid result at time 1339106540 (..\..\..\rosetta_source\src\game\application\novice\boinc\Boinc.cc:407)
SRVR_THRD sending: 308854 992848 score
Autosaved puzzles/0000992848/0000308854/default/autosave.ir_solution.
Autosaved puzzles/0000992848/0000308854/default/autosave-best.ir_solution.
Autosaved puzzles/0000992848/0000308854/default/autosave-recentbest.ir_solution.
Autosaved puzzles/0000992848/0000308854/default/autosave-creditbest.ir_solution.
Autosaved puzzles/0000992848/0000308854/default/autosave.ir_solution.
Autosaved puzzles/0000992848/0000308854/default/autosave-best.ir_solution.
Autosaved puzzles/0000992848/0000308854/default/autosave-recentbest.ir_solution.
Autosaved puzzles/0000992848/0000308854/default/autosave-creditbest.ir_solution.
SRVR_THRD sending: 308854 992848 group_score

Dev:
core.pack.interaction_graph.interaction_graph_factory: Instantiating DensePDInteractionGraph
core.pack.pack_rotamers: built 263 rotamers at 10 positions.
core.pack.pack_rotamers: IG: 110744 bytes
delta_score: -94.8604
Playing sound: 3
SRVR_THRD starting solution data upload...
SRVR_THRD finished solution data upload. took 2.9856 seconds.
SRVR_THRD sending: 308854 992797 group_score