First, I want to say thank  you for any help on this as I am at my wits end at this point.
Quick prologue, I have had a few intermittent DNS issues the last several days with webpages not loading properly across my whole network, once I discovered it was across the whole network switched my DNS servers to from my ISP to openDNS and solved the problem. Except one computer kept dropping from the internet. It was late and I left it.
 
Now to present time, yesterday I decided to re-cycle the router and bam all my problems came to light. Now I am currently getting either one of two errors. DNS cannot be resolved or IP conflict detected. Which either of these I am at a loss. This setup has been running solid for 2 months and before that on my old FIOS router for 2 years!
 
Physical setup:
FIOS MI424WR-Revision-I (bridged via this guide) Link
RTN-66U Router-> DHCP to all client computers.
Original Logical setup:
FIOS MI424WR- 192.168.2.1
RTN-66U 192.168.1.1
DHCP Client list: 192.168.1.2-192.168.1.249
Both on subnet 255.255.255.0
 
Once I received the IP conflict I tried making some changes and this is current setup.
FIOS MI424WR- 192.168.2.1
RTN-66U 192.168.3.100
DHCP client list: 192.168.3.102-192.168.3.249
Both on subnet 255.255.255.0
 
I have had briefs moments of connectivity once I call verizon to release my DHCP lease  but after 20-30 minutes it then goes back into this cycle of either saying DNS cannot be resolved or IP conflict detected bv the router and according to my logs on the RTN-66U it keeps saying LAN subnet is on the same as WAN subnet or DHCP from ISP did not respond.   I am starting to think the router maybe going bad as if I reset the FIOS router, the internet actually works, haven't tested on how long as I have been trying to trouble shoot getting it to the router.
 
Things tried:
Updated firmware on RTN-66U
Reset default settings/re-configured router.
Recovery MODE flash to default firmware then udpateded to most recent.
Only plugged in a single wired computer with FIOS, and the RTN-66U.
Reset to ISP DNS or tried again OpenDNS
 
I am at a loss and would appreciate any help and again thank you for your time.

Just got an idea while at work, but possible the DHCP service on the FIOS router is messed up and somehow handing out IP addresses? Even though the setting is set to off.

Just as an informational FYI, you are creating a network loop. This can and will cause issues with anything from DHCP addressing to DNS resolutions and more subtle problems. I seriously don't recommend going this route using that linked configuration for network bridging.
 
That being said I would not suggest using the 192.168.x.x/24 subnet if your FiOS router is using that for it's internal addressing. Use the 10.x.x.x/8 subnet instead. Separate the entire private class IPv4 range absolutely and begin troubleshooting from there. IP address conflicts are because of an address assignment with the same IP address of another device on the network. Detection of these will be made by one of the two routers you are using. Disabling one DHCP server in either the FiOS router or the ASUS router will help resolve it providing that the IP address assignment is passing those DHCP request packets through to the other device, which is normal unless the firewall is blocking that UDP packet. Normally that does not occur. Having multiple DHCP servers will lead to problems. Devices would get an assignment from one range, then possibly a different range and have routing issues depending on which range they get and where it's being assigned from. This exhibits intermittent DNS/routing errors and bad network performance.
 
Again I don't suggest bridging the FiOS and the ASUS together in the method linked in your original post. You can do whatever you feel you want to but it will cause problems as you are experiencing.
 
Normally you should only have your FiOS router and any internal router linked in a serial type of connection. Should look like this:
 
(Cable/FiOS point of presence box)----> FiOS router (LAN port) ----> ASUS WAN Port ----> Devices (connecting through the ASUS LAN ports).
 
The way it seems that the article provided is showing that really is (in my opinion) going to cause problems looks like this:
 
(Cable/FiOS point of presence box) ---> FiOS router (LAN Port) -----> ASUS WAN Port ----------> Devices (Same physical Segments)
                                                          FiOS Router(LAN Port) -----> ASUS LAN Port  ----------> Devices (Same Physical Segments)
 
If you notice there will be a loop present as you have your FiOS router looped via the ASUS router back into itself and the broadcast domains will be pushing packets through the interfaces into your devices.
 
Just something you may want to consider.
 

Nexillus
James_L,
 
I spent almost 12 hours in the last two days (in between work) trying to get my network back up and you come in and help me get it back up so quickly! You have no idea how appreciative I am. Thank you so much. I followed what you said and booted right up and everything worked! Now, lets hope it stays and I have verified the DHCP server is off on the FIOS router and I made sure by applying it again.

Glad to see you are up and running again. Keep me informed about the status of your connection just in case. I'll monitor this thread for the next few days.

XrayMan beat me to the post and thank you again James and thank you XrayMan! :)

Nexillus
Everythings been working great! Thank you again :)

You're welcome. Glad the solution is stable.