Capture not processing any data with the messages "A portion of the redo log could not be parsed" (4299796)

Event_log shows the following messages:

Process exited sp_ocap  (for o.webdb) [pid = 14508] - exit(1)
Warning: 10727 - Possible log wrap at activation 168, log sequence number 6449, offset 58379820 [sp_ocap/14508]
Warning: 10751 - log wrap detected [sp_ocap/14508]
Notice: Begin record skip at seqno=6449 offset=58379820 [sp_ocap/14508]
Warning: A portion of the redo log could not be parsed [sp_ocap/14508]:

In SharePlex 8.6 or higher, the following messages may show up which are more prescriptive:

Error    2016-07-22 18:07:40.256451 12563 2606753536 Capture: [SP-OCT01001] Unable to find archivelog with sequence#: 54460 (thread: 1).  <CAUSE> SharePlex was unable to locate the redo/archive log for sequence 54460 in the database location or under the directory defined by SP_OCT_ARCH_LOC parameter.  <ADVICE> Restore this archivelog to archive location if missing or set the file's location using SP_OCT_ARCH_LOC.  Make sure it is not compressed then restart capture.  See 'http://advice.shareplex.com/SP-OCT01001' for additional advice and support.   (capturing from source_SID) [module oct]

"show capture detail" output from sp_ctrl shows that nothing is processed:

sp_ctrl (gsbdb:2201)> sp_ctrl (gsbdb:2201)> show capture detail

Host: gsbdb
                           Operations
Source     Status            Captured Since
---------- --------------- ---------- ------------------
o.webdb    Running                  0 10-Oct-07 05:02:07

   Oracle current redo log          : 6473
   Capture current redo log         : 0
   Capture log offset               : 0
   Last redo record processed:     
        None