Cisco Switching/Routing :: RV120W Blocks DSL Modem Configuration?

I work for a small pharmacy that uses a Cisco RV120W router to separate hospital VPN traffic from general internet traffic. The VPN traffic is redirected to a dedicated T1 line (Or T-something, I wasn't involved in the actual setup of the VPN) connecting our store directly to the local hospital, and general internet traffic gets redirected to a ZyXel PK5000Z DSL modem (We have Qwest/CenturyLink 7m/768k). The DSL modem is running the latest version of our ISP's custom firmware.
 
Prior to installing the VPN and RV120W, LAN traffic was handled with a basic D-Link DI-604 wired router. The router itself was configured with an IP of 10.100.100.254 (With all LAN clients assigned DHCP IPs in the 10.100.100.XXX range) and "WAN" IP of 192.168.0.4, and the modem configured with a LAN IP of 192.168.0.1. The router was connected from it's WAN port to one of the LAN ports on the modem.
 
The modem has it's own built-in router, but the store owner wished to have an "extra layer of protection", so to speak, and had the D-Link router installed to serve that purpose. Prior to connecting the VPN, a second router was admittedly redundant and unnecessary. However, now that we have the hospital VPN, a second router is REQUIRED to properly separate the VPN traffic from other internet traffic, since the router built into the DSL modem doesn't have the capabilities to perform this task (We had already attempted to operate the VPN over DSL...it failed miserably and spectacularly. A dedicated T1 was the only reliable option).Anyway, when installing the RV120W, we duplicated every possible setting from the old router, including configuring it with a LAN IP of 10.100.100.254 and a "WAN" IP of 192.168.0.4 and connecting it in exactly the same fashion as the old router (Modem LAN to Router WAN). Essentially, the RV120W was set up exactly the same as the old D-Link router, just with the added VPN functionality.
 
The problem is this: ever since installing the RV120W, we are no longer able to access the DSL modem's administration page (http://192.168.0.1). We were able to do this without any trouble whatsoever with the old D-Link router, but the RV120W seems to be blocking it somehow. Any attempt to load the modem administration page just forever sits at "Waiting for 192.168.0.1...". It never times out, it never shows any error messages. It just sits there, forever trying to load the page, showing nothing but "Waiting for 192.168.0.1..." at the bottom of the screen.
 
Now, we know for a fact that it is NOT a problem with the modem, because if we connect a computer directly to it via ethernet (Completely bypassing the RV120W), the administration page loads perfectly fine. And, admittedly, we could configure the modem in this manner whenever required. HOWEVER, the modem is located in a rather inconvenient location (In the ceiling, sitting on top of a ceiling tile), and having the ability to remotely manage it like we could before would definitely be something we want to be able to do again...especially since there are plans in motion to install new pharmacy equipment that will require us to do a ton of "trial and error" configuration to the modem.The RV120W has been updated with the latest firmware, yet the problem still persists.