Thak you, Howard
No, that's MDB_MAP_FULL. This particular error means some other process opened the environment and increased the mapsize. Currently back-mdb doesn't handle this error code because nobody should ever be doing that to an OpenLDAP installation.
I found a bug report filled years ago that seems to be related to this: https://bugs.openldap.org/show_bug.cgi?id=8179
Also, I think I didn't understand what you mean with "nobody should ever be doing that to an OpenLDAP installation". Shouldn't I use mdb as OpenLDAP backend?
Regards, Leonardo Lopes