I am not sure whether KiXtart still is maintained, but I still use it extensively at home for running several system checking scripts.
This morning I added a new SSD to my Windows PC, a 4TB version, with drive letter D.
And it appears that my syscheck script returns a negative value as free space for this drive.
So I made a very simple check script:

$DriveSpace = GETDISKSPACE("D:\")
?? $DriveSpace

And indeed a negative value is returned.
The returned value should be 3,675,641,319,424 bytes, but I get -705,473,820 KB
Sounds this familiar to anybody?