I noticed that one of my Linux boxes still had a WU that was a few days old. boincmgr shows it 30% complete and "Waiting to run".

Checking the log file, I see only two messages for that WU:

=====================================
2007-08-06 09:27:01 [rosetta@home] Starting
1utx__BOINC_SYMM_FOLD_AND_DOCK_RELAX-1utx_-foldanddock__1878_1543_0
2007-08-06 09:27:01 [rosetta@home] Starting task
1utx__BOINC_SYMM_FOLD_AND_DOCK_RELAX-1utx_-foldanddock__1878_1543_0
using rosetta_beta version 573
=====================================


The client_state.xml file has this:
=====================================
<active_task>

<project_master_url>https://boinc.bakerlab.org/rosetta/</project_master_url>
<result_name>1utx__BOINC_SYMM_FOLD_AND_DOCK_RELAX-1utx_-
foldanddock__1878_1543_0</result_name>
<active_task_state>8</active_task_state>
<app_version_num>573</app_version_num>
<slot>1</slot>
<scheduler_state>1</scheduler_state>
<checkpoint_cpu_time>8846.305156</checkpoint_cpu_time>
<fraction_done>0.307476</fraction_done>
<current_cpu_time>8857.308483</current_cpu_time>
<swap_size>252416000.000000</swap_size>
<working_set_size>152301568.000000</working_set_size>

<working_set_size_smoothed>152301568.000000</working_set_size_smoothed>
<page_fault_rate>0.000000</page_fault_rate>
</active_task>
=====================================

That is an <active_task_state> that I had not seen previously. Searching for the meaning of it, I found a thread that listed the defines for <active_task_state> which included
#define PROCESS_IN_LIMBO 8

That sounds like the catch-all "an unknown error has occurred". Any suggestions before I stop and restart boinc and/or the computer?