The variable should be outside the quotes.

    CurrentDb.Execute "UPDATE tblVehicleList SET HCOrder=" & X

Maybe I haven't had my coffee yet, or I don't use CurrentDB.Execute like that, but isn't that going to set every record to X every time it goes to a new record? Resulting in all of them being the same?

This is simpler :P.
While Not Rs.EOF
X=X+1
rs.edit
rs!HCOrder=X
rs.update
rs.movenext
wend

Unless you're trying to make them all the same for some reason. But thats not what I think when I hear "reorder list"

Adam,
You are exactly right on both counts. It updated that field (I think to the total number of records) on every record. And it was not what I wanted.

What I ended up doing was adding a new field to the table Called NewOrder and then using the following code. So the first part of the code updates the field NewOrder with sequential numbers, then it updates the field HCOrder with those values. It could be that your code would do it all at once. Here is the code I finally got to work for me.

    X = 0
    While Not IsNull(VehicleID)
        X = X + 1
        NewOrder = X
    DoCmd.GoToRecord , , acNext
    Wend
    
    DoCmd.GoToControl "HCOrder"
    DoCmd.GoToRecord , , acFirst

    While Not IsNull(VehicleID)
    
        HCOrder = NewOrder
        DoCmd.GoToRecord , , acNext
    
    Wend