A) For incremental backup jobs
Verify Set Detail Information
Data for VMVCB::\\vCenter\VCGuestVm\(DC)DC1(DC)\vm\Windows 2012\Windows 2012\Windows 2012.vmdk is corrupt.
Final error: 0xe0009578 - Unable to copy the virtual machine disk using the VMware VixDiskLib.
Final error category: Resource Errors
For additional information regarding this error refer to link V-79-57344-38264

Please run a full backup.
1. Open Backup options and add a Full backup task as below.

2. Run full backup task.

VMDK file size for incremental backups have been extended compared to base line backups. Backup Exec cannot merge VMDK files of different size.
For example:
Extend VMDK file size from 40GB to 60GB before incremental forever backup.