Unfortunately, this one may be difficult to narrow down. However, I would verify the following:
1. For the Web/SA issue (i.e., not being to open the page), my assumption is that you mean the page won't load. In that case, the first thing I would do is restart IIS and see if that clears up that problem.
2. For the failover, the I would recommend that you walk through the configuration steps and see if you can nail down where the problem may reside:
http://www.cisco.com/en/US/docs/voice_ip_comm/unity/5x/failover/guide/ex/5xcufge010.html
Note: You didn't mention the version of Unity so this is for 5x and 7x. I don't think the config is too much different 4.x and higher. Anything older than that, you may want to look at that version specifically just in case.
3. Verify network connectivity (IP and DNS) between the servers.
Hailey
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