Does it happen each and everytime that you failover?
would really need to know what the actual error you are seeing on the screen
whether Search.asp works or does that fail also
would also need a dtrace of w3wp as well
As Jesus asked, check if search also having similar problem? archiving/retrival with http client happening correctly when this appears on server? If this problem solves with IIS reset then also look option disscused in another forum.
Can you please update this thread by either flagging some of the postings above as having resolved your issue or update the ticket with more details as to your issue? Doing so helps those who are helping direct their help to where it is most needed first.
Thanks in advanced.