well, so far on my 260, there has been 12 errors since 24th august- all with this error:
<core_client_version>6.6.20</core_client_version>
<![CDATA[
<message>
- exit code -6 (0xfffffffa)
</message>
<stderr_txt>
VLAR WU (AR: 0.029390 )detected... autokill initialised
SETI@home error -6 Bad workunit header
File: ..\worker.cpp
Line: 144
</stderr_txt>
]]>
however, looks like for most of these, there's someone else who has errored on them as well, but usually someone with very long compute time (ie non CUDA i guess) that has completed the WU.