Netopia VPN to Cisco PIX VPN????

I'm attempting to define/connect an IPSec VPN from a 3386-ENT Netopia
router to a Cisco PIX 501 unsuccessfully. It appears that when the
remote router (Netopia) initiates the connection the Cisco sees the
request and immediate dumps it.

I've checked & rechecked all the configuration parameters to assure
that they match for all that appear to be definable.

Has anyone accomplished this before? Anyone familiar with the PIX
firewalls... anything that might cause this rejection?

Please advise what one could look at?

Thanks