The transaction failed to commit for an unknown reason   

We are working on component implementing integration between the Exchange 
(2003) and our product. We have uncommon problem with one customer. We try to 
add new item to user’s calendar and receive exception “The transaction failed 
to commit for an unknown reason. The transaction was aborted.” when calling 
method CDO.AppointmentClass.SaveToContainer(String ContainerURL, Object 
ActiveConnection, ConnectModeEnum Mode, RecordCreateOptionsEnum 
CreateOptions, RecordOpenOptionsEnum Options, String UserName, String 
Password).

We have checked access rights to user mailbox and have not found any 
differences from our usual settings. We have even tried to add everyone full 
access to the user’s mailbox and to the user – no improvements. This user is 
not is not a membed of the Active Directory protected groups. This user and 
his mailbox were created by customer. We added new user and mailbox and did 
not have any problems with him.

Here is some code. Our application is Windows Service written on C#, .NET 1 
and uses COM interops to work with CDO objects.

ConnectionClass con = new ConnectionClass();
con.Provider = "ExOLEDB.DataSource";
// xchgPath = “//./backofficestorage/SERVER_NAME/MBX/USER_NAME/Calendar”
con.Open(xchgPath, "", "", (int)ADODB.ConnectOptionEnum.adConnectUnspecified);
appt = new AppointmentClass();
...
appt.Fields.Update();

// exception !!!
appt.SaveToContainer(xchgPath, con, 
      ADODB.ConnectModeEnum.adModeReadWrite, 
      ADODB.RecordCreateOptionsEnum.adCreateNonCollection, 
      ADODB.RecordOpenOptionsEnum.adOpenSource, "", "");

date: Fri, 7 Mar 2008 00:27:00 -0800   author:   Alexey Kruglov Alexey