Ok try this, I was thinking about it, and against my better judgement I installed BA on my old laptop again to check.
If you close BA by clicking the X in the top right hand corner, it does not close BA, but instead it remains in the system tray, if you subsequently try to run BA again by double clicking your shortcut, it will give the javascript error everytime. If however you close BA by going to the options (
the little gear icon top left) and selecting 'quit', (
which does actually close BA), and then subsequently try to run BA again by double clicking your shortcut, you will not get the javascript error. I tried this 10 times, and it was reproducible 100% of the time. Try it.