Since windows wants to reformat the drive the ISO is stored on when you try to mount it, download 7-zip from
http://www.7-zip.org/download.html. Install it in Windows 10 on Parallels on your Mac. Use 7-Zip to extract the ISO to a folder in parallels or on an external drive. If 7-zip cannot extract it, you will probably need to download the ISO again. Then extract it with 7-zip and find BWCheckDisc.exe inside that folder and run it. It checks the integrity of the download and extraction. It will take a while. If no bad files are found, then use setup.exe in that folder to install BW.
If you have a slow internet connection and only one or two bad files are found and the rest are good, pm me and I could help you just get those replaced without redownloading the whole ISO. Then you could use them to replace the bad files in the extracted folder.