Hi Andy,
I work in Tech support at CBC who are the manufacturers and distributors of Ganz and Computar products and I have come across this problem before.
The web viewer and 'Video server E' both use Java and 'Active X plug-ins' in order to display the streaming video and the problem you've described I have come across before and this was the cause:
When you type your DVRs IP address into a web browser, you are presented with a log in page which is HTML based and you then enter your username and password. Normally, because of a persons Active X settings in internet explorer, you get a yellow bar across the top of IE asking if you wish to install and run the Active X. If you say yes to this, it installs and runs, no problem. If you say no to this at any stage, your PC caches this response and doesn't ask you again. So the next time you try to log in, the PC remembers that you refused the ActiveX download and that you don't want to run the ActiveX from the DVR and throws up the 'page not found' message.
So in order to view the DVR in the web browser, please do the following, (and if I'm teaching to suck eggs or seem patronising in my explanation in any way, I honestly don't mean to be, sorry, just trying to be thorough! )
Install the latest version of Java.
Delete your internet explorer temp files.
From within IE, go to TOOLS, INTERNET OPTIONS, SECURITY, CUSTOM LEVEL and then either 'enable' or 'prompt' for the downloading, installing and running of ActiveX controls. Personally I 'prompt' for anything to be downloaded and installed and just 'enable' everything else. That way, and in my view, if I have allowed a download and install when prompted, I've already given permission for it to run and don't wish to be asked every time to run it. However, each to their own and the way you configure this is up to you, but an ActiveX plug-in MUST be downloaded and allowed to run in order to connect to the DVR. I believe it is an unsigned ActiveX plug-in.......But you can trust it, honest!
Let me know how oyu get on,
Cheers,
Mark.