Outlook 2003 Disconnected when accessing over VPN

I have got 2 users who use a VPN to access Exchange using Outlook 2003 in cached mode. The VPN client is Sonicwall. Both of them access only this 4 or 5 times a month and about 2 or 3 of those times they call me saying they cant connect or they were connected and got kicked out and it will not reconnect. I have serched for this issue everywhere and it seems to me that the problem is with "Too Many MAPI connections". Below is the error message that I am getting:

Task "Microsoft Exchange Server" reported error (0x80040115): "The connection to the Microsoft Exchange Server is unavailable. Outlook must be online or connected to complete this action."

Task 'Microsoft Exchange Server' reported error (0x8004011d): 'The server is not available. Contact your administrator if this condition persists.'

I am using SBS 2003 with Exchange 2003 Service Pack 2. Thanks for any help.

Can you tell us whether your users have thousands of reminders open? You can check some articles about increasing the mapi clients. I guess you have the exact error to do a google search. The account that we were using, we used to encourage that person to click on dismiss all. Reminders of meetings 2 years past does not seem helpful. It seems to happen inside their office and only to one user and for that one user at any workstation.