I just had this same problem. Here's a link to the posting that helped me get my Linksys router working properly with my Cinci Bell Westell 7500 set to Bridge-to-Bridge mode:
»[modem/router] 7500 won't stay in Bridge mode
Skip down to the entry from Bytebender that starts with "That's what it sounded like to me too". It's the "tip" in that posting that fixed my problem.