Well I opened a PMR and they suggested running the R5 Cab file on the WM 6. To cut a long story short we tried that and it also failed though it seemed to go through a bit more through the process. Then we manually uploaded the WM 6 Cab file and overwrote the previous cab file that was there and it installed.
Should have tried this in the first place.
Feedback response number WEBB7CW7PF created by A Lamb on 03/20/2008