REALLY strange Comcast admin page question (EG help!!)

Yesterday i learned that when you bridge your Comcast gateway, you can no longer access it with 10.0.0.1  but instead 192.168.100. 1

I did that, and immediately was taken to the gateway's web page.  I thought all was fine.  BUT when I went to sign in with 'admin' and my changed password, I received "ACCESS DENIED!I 

I tried several times, no luck.   

Then I connected the gateway directly to my computer via Ethernet, rebooted the gateway and when my Internet came back, I accessed the gateway via 10.0.0.1.   

The sign on page popped up, I used 'admin' and my previously changed password and got right in immediately!!!

I then connected the gateway back to my router, rebooted the gateway, accessed it via 192.168.100.1 and once again it said my access was denied.   For some reason when using the two different URL addresses it wants two different passwords.   I tried  'admin' and 'password' and that didn't work so I have no idea what it's looking for.  And if I go through the hassle of restoring back to factory settings,  I'm pretty sure the same thing will happen.  It'll work great when connected directly to my computer,  after bridging and going through my router it will not.

Do you have any idea what's going on here?   I always appreciate your expertise.  Thanks