Port forwarding just stopped working

[#1]

Hi all, I have posted this on Utorrent forum, but wondered if i would get any help here. Please dont misunderstand, this problem with port forwarding is not just with Utorrent, I have tried a web server too..
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I have used Utorrent for well over a year with no problems. I set the port forwarding up my self with out any problems. I recently bought a Buffalo NAS and ended up making some changes to my network..
I have a Solwise SAR110 router, I subscribe to Plusnet ADSL. I use a Netgear wireless firewall router WGT626 (i use windows firewall, but have the exception set for Utorrent and a web server).
Previously I was using the netgear just as a hub, but on getting the NAS I changed config to using the netgear as a router going in to my other router. Utorrent was still working fine at this point. In the same week I upgraded to 1.7.7 of Utorent.
Later on in the week all of a sudden I was no longer able to log in on Utorrent. After checking the test to see if the port was forwarded correctly, I found it was not. To be fair, at this point I think the port forwarding rule was now invalid as it was from when I was using my hub, so the rule in the solwise was specifying my PC's static IP address. I have now changed this so that I have a port forward rule in my netgear for my PC ip address (tried with and without UPNP), I then set another one in the router forwarding the port back to the netgear.
I have a lot of trouble getting the port to forward. Occasionally it will be open if i try an online test, but it blocks within about 30 seconds.
I have now tried elliminating the netgear and using a ethernet cable from pc to solwise (yes i changed settings and rules) and i was still unable to forward a port. I have also been testing by running a webserver on my pc on a similar port, and this is intermittant too.
The port only seems to open after i make changes in the SAR110 but closes very quickly.
I am over my useage allowance this month with Plusnet, but I mailed them and they say they do not block ports.
I suspect the solwise or plusnet..
Does anybody have any ideas or similar problems please?

[#2]

What is the reason for usng two routers? Even with NAS attached you'd be better using one router and a switch (which would cost about £10). 
However, in your situation, I would check to see that each router is in a different private IP address range.  If they're both in the same range (e.g. 192.168.0.x) you could run into problems. (Although I see you've tested by taking the Netgear out of the equation so this may not be relevant).
In the Netgear you can do this by going to LAN IP settings and changing the address range.  You could try entering something like 10.0.0.10 to 10.0.0.50 and see how you go.
One other thing - have you checked the configuration of your PlusNet firewall and your Safe Surf settings (login required)? 

[#3]

Thanks Paul. I checked my safe surf is off and firewall is also off.
I really dont have any other ideas seen as i have tried without the netgear.
I even reset defaults in my router without netgear and basic ADSL settings + port forward rule but no luck.