Unable to delete logical drive in NT4

I have a number of logical drives using NTFS in NT4 Workstation. I want to delete two of the drives in order to enlarge one and reduce the size of the other.

When I try to delete or format either drive in Disk Administrator an error msg appears saying that the volume is in use by another process.

It is not in use by any process and all files have been deleted from it.

There must be a flag set somewhere indicating that the volume is in use. How can I resolve this problem and delete the drive?

Thanks

Rod Fletcher