When attempting to Migrate a GEN6 settings file to a GEN7 settings file, the Migration tool throws an "Internal Server Error" on the browser and doesn’t provide a migrated settings file to use.

Global Bandwidth management not supported in GEN7 appliances. This is expected to be fixed in the upcoming release on Migration Tool v 4.35.1
Disable BWM (Bandwidth Management) on the GEN6 Firewall and then export the settings file from the firewall to use in the Migration tool.
To disable BWM in your GEN6 Firewall, Please access the UI.
Go To Firewall Settings > Bandwidth Management > Set to NONE.
Save the configuration , Export the settings file from the firewall and then use this file as the source settings file in the Migration tool.