Hi,
How are you powering the drive and\or adapter ?
I have had mixed results using a USB to IDE\SATA adapter over the years...
Is this drive IDE or SATA ?
If the drive is IDE you might try setting the jumpers to "Cable Select"...
Master might confuse the adapter...
It is possible that there is something about the permissions\ownership of the drive that is causing problems, but I suspect that the underlying problem is that the machine was shutdown and the drive originally removed, while Fast Startup was enabled...
This is almost a sure fire way to trigger errors...
One thing you might try is to use a bootable Linux based File Explorer of some type...
Older versions of Parted Magic have this feature, and are available for free as a ISO that will burn to a bootable CD or Flash Drive...
The newer versions require that you purchase it to create the bootable media...
If nothing else, this may enable you to copy the files on the problem drive to something else... Parted Magic may also have a fdisk\chkdsk type feature that may work better...
BTW... The System Reserved Partition is probably the 300-500mb "Recovery" partition where the WinRE "Repair\Recovery" files are kept...… I'm sure your drive is more like 500GB or larger, not 500mb... correct ?