got 2 pc's that are giving me an error saying that your exchange administrator has blocked the version of outlook you are running. I did no such thing and both Outlook versions are 2003 with exchange 2007, over 400 people and those are the only 2 pcs. Any idea?

Please check the use mailbox MAPI function is set Enable! EMC>recipients>mailbox>select user mailbox properties>mailbox feature

Did you ever resolve this issue? I am having the same problem with an Outlook 2003 client attepting to use RPC over HTTP. Thanks.

I had this same problem with Outlook 2003 connecting to exchange 2003. After 2 hours of tech support from Microsoft, we found the issue. Using ADSI Edit, pull up the value of "protocolSettings", for the account that was getting the blocked error message, it had a value of "MAPI#0#######", all others had no value set. I removed the value, restarted the information store and the error went away!

Pretty sure you don't need to restart the information store. By pretty sure I mean I just tested it.Just my $0.02

I to Had this Problem. The solution Mokingham posted worked for me.