There should be no need to use a bridge on the router for the WAN connection on a single port.
Also assuming your using vlans did you read this guide… ------> http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1
Post your confiig for both devices.
/export file=anynameyouwish ( minus device serial number, any public WANIP information, keys etc. )