In this thread is commented the same error
https://openacs.org/forums/message-view?message_id=179348
Somebody has testing this code for solved the error with the cache aolserver?
"I just noticed that PostgreSQL has a memcached interface, pgmemcache. Also, Harish Krishnan provided a very small Tcl API to memcached back in Aug. 2005"
Bye.