I was having the same issues too. I followed the steps dotted all over the internet and was getting stuck in exactly the same place. No matter how hard I tried, I just kept getting the 'invalid filename' issue.

Eventually I figured it out - the way that Netgear/Virgin have blocked firmware updating is to break the filename checking page so it doesn't accept any files. What we need to do is bypass the filename checking code so that the firmware upgrade system can then handle the file, and we're going to do this by manipulating the web page using a tool called Firebug.

Here is the solution:

1) If you haven't already got it, install Mozilla Firefox 3 (there is good reason for this - I'm not just shamelessly plugging it! :P).
2) Install the 'Firebug' extension for Firefox from https://addons.mozilla.org/en-US/firefox/addon/1843 and restart your browser when requested.
3) Navigate to your router's admin page, and fill in your login details (if you don't know them, it's likely to be the one written on the bottom of your router).
4) Navigate to the router upgrade page (the one where you select the firmware to upload' and select the location of the firmware file, like you would normally. Now, instead of clicking the 'Upload' button, press F12. This should bring up Firebug in the bottom quarter of your screen.
5) Now, click the

6) It looks like Netgear have actually stripped out the real checking code so it can't be used, so we'll need to fool the page into thinking everything's fine and dandy with the filename so it can update the firmware. Click where it says "return checkData();" and replace it with "return true;".

7) Finally, click the upload button. The router should now accept the file and start updating.

And hey presto! You have a non-nargled wireless router with the latest firmware!

Use only INTERNET EXPLORER for firmware update as it wont work with mozilla firefox, mine updated perfectly fine

Just change the filename to match the router and version number with an img file extension. for example on a netgear WRN2000 router put the file name as WNR2000-V1.2.3.7NA.img i had the same problem with invalid file name and this cleared it up.

1. Please verify the model and version of the router underneath it.
2. Go to http://kbserver.NETGEAR.com/downloads_support.asp and select the model of the router.
3. Please click on the appropriate version of the router.
4. Select the link of the latest firmware. Please click on the button Right-click and Save to Download. For the WGR614v9, here's the link ftp://downloads.netgear.com/files/WGR614v9-V1.2.6_18.0.17NA.chk
5. Save the file to the Desktop.

Note: Please perform firmware upgrade with wired or Ethernet connection only. Before you upgrade, write down all current settings as you need to enter them manually after upgrading.

6. Using the computer hardwired on the router, open any web browser like Internet Explorer or Netscape Navigator.
7. Connect to the router by typing http://routerlogin.com/basicsetting.htm or http://192.168.1.1 in the address field and click Enter or Return key.
8. A window will prompt for a user name and password. The default username is "admin" and the default password is "password".

Note: If it does not take password as the password, you might have changed it when you have run the NETGEAR Setup CD so please try other passwords. If you cannot remember the password, you need to reset the router and run the Setup CD to reconfigure it.

9. Click on Maintenance and then Router Upgrade.
10. Click Browse and locate the upgrade file in your Desktop. Click Upload.
11. Please wait for the router to reboot.
12. Reset the router.

a. Please push the reset button at the back of the router and release after 30 seconds.
b. Unplug the power adapter for 10 seconds and then please plug it back in.