I had this problem, too. I had about 250 devices Partially Collected because CW could not download the vlan.dat.
I just started a netconfig job for those devices.
The job ran the following command:
vlan database
vlan 666 name CiscoBug
exit
vlan database
no vlan 666
exit
Works fine for me =). The vlan.dat keeps on flash even if u delete the just created vlan with the "no" command.
Patrick