I had this issue after trying to reset the admin password – ZeroShell web interface locked up and after a reboot got stuck at “Recovering LDAP DB”.
In case anyone still having this issue, I fixed mine as follows:
Boot to any Live CD.
Mount the partition with the affected configuration.
cd /mnt/sda1/_DB.001/var/openldap-data
sudo mkdir bak
sudo mv __.db.00* ./bak/
sudo reboot
ZeroShell reboots okay but not sure what part of LDAP configuration is affected.