I've had this happen twice and grabbed the log.txt this time. Client closes on loading a previous save from within solo, attempting to open previously saved solo (not loading anything as a guide as indicated in log.txt below).

Mac OS 10.6.8 devprev.

SRVR_THRD starting solution data upload...
Tool on_action_complete called
SRVR_THRD finished solution data upload. took 4.63967 seconds.
SRVR_THRD sending: 99169 993229 group_score
SRVR_THRD sending: 99169 993229 score
SRVR_THRD sending: 99169 993229 improver_score
SRVR_THRD getting notifications...
SRVR_THRD sending play event log...
Autosaved puzzles/0000993229/0000099169/default/autosave.ir_solution.
SRVR_THRD sending: 99169 993229 group_score
SRVR_THRD sending: 99169 993229 score
SRVR_THRD getting notifications...
Autosaved puzzles/0000993229/0000099169/default/autosave.ir_solution.
Autosaved puzzles/0000993229/0000099169/default/autosave.ir_solution.
Error reading upload_tmp_988948_1291658941.ir_solution; expected SOLN, got ion:.

Error reading upload_tmp_988948_1291658941.ir_solution; expected SOLN, got ion:.

loading solution as guide: puzzle_993229_time_1346366874.ir_solution

ERROR: base_ref_info->sidechain_locks.size() == sequence_mapping.from_reference().size1()
ERROR:: Exit from: /Users/jflat06/foldit/mini-interactive-main/rosetta_source/xcode/../src/interactive/util/ReferencePoseInfo.cc line: 418