When attempting to add a directory group to a provisioning group "List Error: Unknown Cause" error is displayed.
"List Error: Unknown Cause"
This issue is when a problematic group document in the names.nsf is preventing all group documents from being enumerated. This issue can be caused by a group that is missing the ListName field from the document properties.
To work around this issue find the problematic group and delete the group document from the names.nsf.
This issue has been addressed as part of the following release:
Enterprise Vault 10.0 - Release Details