Update:
I set the second vmdk file (CAS-SQL-02-Vista-000001.vmdk) to the actual size of the delta file (CAS-SQL-02-Vista-000001-delta.vmdk) as it stands.
I then re-added this file as a existing VHD on the machine.
In settings when I re-added the drive the size appeared correct (350GB) but once it saved it reverted back to the 175TB which is obviously wrong.
I now get the error on power on:
Failed to power on virtual machine CAS-SQL-02-Vista. The file specified is not a virtual disk
Other Info:
[root@CASSELLESX-01:/vmfs/volumes/551efb4a-013401c2-43af-d4ae5266c08e/CAS-SQL-02-Vista] vmkfstools -x check CAS-SQL-02-Vista.vmdk
DiskLib_Check() failed for source disk 'CAS-SQL-02-Vista.vmdk': The destination file system does not support large files (12).
[root@CASSELLESX-01:/vmfs/volumes/551efb4a-013401c2-43af-d4ae5266c08e/CAS-SQL-02-Vista] vmkfstools -x check CAS-SQL-02-Vista-000001.vmdk
Disk is error free
