Had a slightly similar problem -- Had a user, who was made redundant. I disabled their account and gave mailbox rights (permissions) to one other staff to access the mail still coming in. It was all working well until, I gave the same rights to a second user.
After doing this I recieved the "Information store could not be opened" error messsage. This error message came up irrespective of the user logged in, and the workstation to which they were logged into. Then I logged in as administrator - same problem.
I decided then to see if the disabled user could access their mail, so I re-enabled their account and recieved a similar (but different) error message, " Unable to open your default mail folders. You do not have permission to log on".
This spawned a new google search, and eventually I ended up on the microsoft knowledge base. They suggested a few things, which I skipped, but the step which seemed most relevant under the circumstances, was to clear the cached credentials which the exchange client uses to log onto the workstation.
To do this:
[] Log onto the troublesome workstation as the user (not admin)
[] under Control panel open the mail icon.
[] Chose the option 'setup email accounts'
[] Choose to view/change existing email accounts.
[] Click the 'Change button'
[] Click the 'More settings' button
[] Click the 'Advanced' tab
[] In the drop down box labeled 'Logon network security'
Change it to 'None'
[] This may ask you for a password - enter it or cancel it - does not seem to matter.
[] Finish the whole process, click yes, save/ finish etc then open outlook
[] This time you should be prompted for a password and a domain to log onto. Enter these in.
From now on, every time you logon you will be asked for a password. To fix this, follow the above steps, but instead of leaving the 'Logon network security' field left to 'none', change it back to 'Password Authentication'.
This should essentially clear any previously cached passwords and overwrite them with the current user password. And hopefully fix your problem.
NB: Here is the Microsoft link:
Error Message: Unable to open your default Mail folder.
Cheers.
