Format dvd-rw

Using Inspiron 531 with wimdows vista.  Recently purchased box of Imation DVD-rw DISKS  120MINS  4.7gb  4 X 10.  On trying to format these the format appears to start all right but approx. two mins later the message comes up "Windows cannot complete the format".  This only happens with Imation disks not with the Verbatim disks I normally use.  Can anyone throw any light on the subject.

many thanks

ron