Port Forwarding not Disabling on R6250 Router

> We are using a Netgear R6250 router [...]

   R6250[v1] or R6250v2?  Look for "Model" on the product label.
Firmware version?  Connected to what?

> [...] the DVR [...]

   Not a very detailed description of that device.

> [...] The port forwarding pointed to the DVR's local address of
> 192.168.1.200.

   What was the actual port-forwarding rule?  (I might guess external
port 80 to internal port 80, but that'd be only a guess.)

> [...] If I use IE, and input our external IP address, it prompts to
> download/install the "dvr_ocx.cab" file.

   Are you running that test from a system on your LAN, or from a system
in the outside world?

> [...] the company verifying our network can see that DVR and file
> download request.

   That suggests that it's (at least) a from-outside-world problem.

   Is there a DMZ server specified on the R6250? (ADVANCED > Setup >
WAN Setup : Default DMZ Server)  Any port-triggering rules defined?

UPnP?  (ADVANCED > Advanced Setup > UPnP)

> Why is the port forwarding still pointing to the DVR when it was
> deleted?

   Defective firmware would be one possible explanation.  If the
port-forwarding rule list is empty, but the router is still doing port
forwarding (and there is no DMZ server specified, and there are no
port-triggering rules, and UPnP is disabled), then a settings reset (and
manual reconfiguration) might be the only reliable remedy.

   A potentially interesting experiment would be to recreate the original
port-forwarding rule, but specify a target server address which is not
in use.  (Reserve one for a fictional MAC address if necessary?)  I'd
expect that to provide a work-around, but it shouldn't be needed.