We're seeing this in the slon logs (we are doing slon archiving as well, 
the slon -a flag):

2015-10-28 07:54:56 PDTDEBUG1 remoteWorkerThread_1: connected to provider DB
2015-10-28 07:54:56 PDTDEBUG2 remoteWorkerThread_1: prepare to copy 
table "abc"."data_set_720"
2015-10-28 07:54:56 PDTDEBUG3 remoteWorkerThread_1: table 
"sch1"."data_set_720" does not require Slony-I serial key
2015-10-28 07:54:56 PDTDEBUG2 remoteWorkerThread_1: all tables for set 
14 found on subscriber
2015-10-28 07:54:56 PDTDEBUG2 remoteWorkerThread_1: copy table 
"sch1"."data_set_720"
2015-10-28 07:54:56 PDTDEBUG3 remoteWorkerThread_1: table 
"sch1"."data_set_720" does not require Slony-I serial key
2015-10-28 07:54:56 PDTDEBUG2 remoteWorkerThread_1: Begin COPY of table 
"sch1"."data_set_720"
2015-10-28 07:54:56 PDTDEBUG2 remoteWorkerThread_1:  nodeon73 is 0
NOTICE:  truncate of "sch1"."data_set_720" succeeded
2015-10-28 07:54:56 PDTERROR  remoteWorkerThread_1: Cannot write to 
archive file 
/usr/local/pgsql/slon_logs/slony1_log_2_00000000000001552202.sql.tmp - 
not open
2015-10-28 07:54:56 PDTWARN   remoteWorkerThread_1: data copy for set 14 
failed 1103 times - sleep 60 seconds
2015-10-28 07:55:04 PDTDEBUG2 remoteListenThread_1: queue event 
1,1587129 SYNC


The archive dir is writable by postgres and the file perms are:
ls -l /usr/local/pgsql/slon_logs/slony1_log_2_00000000000001552202.sql.tmp
-rw-r--r-- 1 postgres postgres 504 2015-10-27 13:18 
/usr/local/pgsql/slon_logs/slony1_log_2_00000000000001552202.sql.tmp


Thoughts?

Thanks in advance