Sometime in the past few days something updated cauldron to set the bash variable $TMOUT to read-only.  The only problem with that is that /etc/security/shell, which is run whenever .bashrc is sourced, tries to set it to 0 and produces an error message about TMOUT being read-only.

Commenting out the assignment gets rid of the message.  It seems to be set to 0 anyway.  

Presumably it is being set read-only to prevent something else from setting it to a nonzero value, but either that something else should be changed or else /etc/security/shell should be changed.