Issue most likely has happened because of index-disks being dismounted without previous warnings.
I now see in eventviewer
Event Type: Error
Event Source: Enterprise Vault
Event Category: Index Server
Event ID: 7264
Abnormal error occurred
Error: The directory is not empty. [0x80070091]
Index: 106A5768273522B458A913AFF8D15B67C1110000DMS/Volume:79830 (Journal Archief voor de VAD4121)
Additionally same event other reports:
The AltaVista index is not open
The index is in a rebuilding state (actually choose Update).
Anyone an idea what to do (besides restoring a working copy and update that?)