Please ensure that the Windows which you have moved to external drive has all the data and apps and nothing is missing.
Proceed only if you have confirmed it.
I suggest you delete the bundle present in Boot Camp. To delete the bundle using Fusion,
Launch VMware Fusion
Go to Window menu > Virtual Machine library .
By this time you should see two VMs listed .
One present in Boot camp volume.
other located in external hard drive.
Select the virtual machine located in Boot camp volume and delete it ( choose the option move to trash ).
To really free up space empty trash.
You may from now on run the VM from external drive itself.
For better performance you may move the Virtual machine back to boot camp volume and run it.
my advice. :
Get rid of Boot camp volume using disk utility ( it does not look it was created using boot camp assistant anyways ) and merge the volume to main mac hd.
once done, move the VM bundle to any location on Mac HD.
IF you are unsure how to merge partitions or use disk utility please refer mac forums or use google.
By doing this you should not see the same error until Mac HD is really out of space.