Microsoft Office Outlook cannot access the specified folder location

My question is whether there is a limit to how many users one can be delegated for? At the moment, we are working on a Small Business Exchange Server 2003. A number of the computers in our office have Outlook 2003, and some have Outlook 2007 installed on them. The problem now is that, I can only see two of the inboxes. With the other users, when I try to open their inboxes from my computer I get an error message:
"Cannot display the folder. Microsoft Office Outlook cannot access the specified folder location. The operation failed. An object cannot be found.”
Even though I have confirmed that these are all set up the same way, yet I can only see two of them. What should I do to correct this?
