Unable to open outlook after moving to Exchange 2003

I just recently installed Exchange 2003 into my Exchange 5.5 site.  I have 4 Exchange 5.5 servers in a single Exchange 5.5 site.  Now I have Exchange 2003 installed in the same site for a migration.  I moved my mailbox to Exchange 2003 for a test.  After the mailbox was successfully moved I opened outlook but got the error

'Microsoft Exchange Server - Sending and Receiving' reported error (0x8004011D): 'The server is not available. Contact your administrator if this condition persists.'

I went into mail in the control panel, unchecked cached mode on my profile.  I then opened outlook again, but receive the error "unable to open the outlook windows.  The set of folders could not be opened.  

I then added a new profile, setup my exchange account, then opened outlook and it worked no problem.  So ok, now I have a solution, but can someone tell me why I got the error to begin with?  And is there a way around this?  I have 300 users I need to move eventually to Exchange 2003, and creating new outlook profiles for all of them is NOT an option.  Any idea what I could check.  I can move some additional test users to try this again.  Could it have happened because I was in cached mode?  Any help is appreciated.

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Guy Hengel [angelIII / a3]Billing EngineerCommented:
you have to go to the mail profile, set the exchange server name, and do the "check now" button once.
MCPJoeAuthor Commented:
ok, I'll try that on another mailbox and update this post.
MCPJoeAuthor Commented:
I just tried this...

I went to mail in control panel, changed my outlook profile back to the one that was giving me the error.  I opened outlook and it worked perfectly.  I'm not sure if the server just needed time to replicate or if by adding another profile with the same Exchange account somehow caused my old profile to start working again.  Either way, I'm going to test this again.  Thanks for the tips.  
PAQed with points refunded (500)

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