Make sure you have the latest version of Data bridge installed, 1.1.8
if you have a previous version installed, uninstall it from the extension manager before installed the newer one.
If you still have the error, try Disabling the preview.
Go to webAssist -> Preferences in the preview section select the option to disable the preview.
The new version of Data Bridge also offers new preview engine choices, you can try selecting one of the other preview engines like WebKit.