The arcade should have been unaffected by the forum change. I don't seem to have any issues viewing it or the scirra account page. Hopefully this is just a temporary hitch but Tom can hopefully look into it.
We are slowly moving everything over to construct.net as the required parts are added but we are not intending to lose any content in the transition.
Could you please make a note of the pages which are failing for you and email support? Hopefully they will be able to help you more.