That sounds rather unlikely since your hastable is incorrect.
The Key can not start with a number.
Like this it works for me
[hashtable]$unassignedDisks = @{
Disk1 = "naa.600507681081001BA8000000000006FC"
Disk2 = "naa.600507681081001BA8000000000006F8"
Disk3 = "naa.600507681081001BA8000000000006F9"
Disk4 = "naa.600507681081001BA8000000000006FA"
Disk5 = "naa.600507681081001BA8000000000006FB"
}
$UnassignedDisks.Disk1
