Migrating to a larger drive (not enough space error)

[Wally]

I'm trying to migrate windows 10 from a 256gb SSD to a larger 512gb SSD.
going through the wizard it is saying that the diskspace required is too small, it requires >1tb ?
Any clues as to why this may be?
I do have a dual boot to windows 7 on another SSD, it sees this but allows me to not select it and only choose the windows 10 on the 256gb SSD ??

Cheers

Wally

Using exclude files to try and get the file size down...It's defining the WINDOWS folder alone at >600GB!