The log of a tape mediapool maintenance run shows
*PTOS50* Can't open index for volume 10 *
The reason is a missing tape index file on the backupserver.
In case of the message above the index file for medium 10 is missing.
The tape index file is located on the backupserver and named Hiback\tape\tape0001.10.
As a workaround you can copy the tape index of medium 11 or the first available tape index:
copy tape0001.11 tape0001.10
Repeat this for all missing tape index files.
Repeat the tape mediapool maintenance run.