Microsoft Exchange DAG backup fails with "[MigrateV6Index]" error

For MS Exchange DAG server backup set created by AhsayOBM version 6, after upgrading the client application to version 7.3.2.0 - 7.5.0.2, when performing a MS Exchange DAG server backup, the following error message is received in the Backup Job Logs :

[YYYY/MM/DD hh:mm:ss] [erro] Unable to do backup, Error= [MigrateV6Index.migrateIndex] Failed to migrate v6 index
[YYYY/MM/DD hh:mm:ss] [info] Start Microsoft Exchange backup
[YYYY/MM/DD hh:mm:ss] [info] Start creating Shadow Copy Set...
[YYYY/MM/DD hh:mm:ss] [info] Shadow Copy Set successfully created
[YYYY/MM/DD hh:mm:ss] [info] End Microsoft Exchange backup
...
[YYYY/MM/DD hh:mm:ss] [erro] null
[YYYY/MM/DD hh:mm:ss] [erro] Backup completed with error(s)