I was having the same problem. Only one user out of 20 users was not
working. I found out that my program was trying to use Microsoft Interop
Assembly 12 on his system when it was suppose to use Microsoft Interop
Assembly 11. We had installed the 2007 interop assemblies which came in the
office 2007 compatibility pack for opening Office 2007 files on his system.
So he had interop assembly version 11.0 and 12.0. Once I uninstalled the
Office 2007 PIA, the program worked again. This is a temporary fix for me
until I can program my software to use the right assembly (if it is
possible). Hope this works for you.

You can check out what versions of assemblies you have installed on that
system at “C:\WINDOWS\assembly” -- Microsoft.Office.Interop.Outlook


"John Yovas" wrote:

We get this error only in one of our users PC with office 2003 we tried re
Reinstalling the Office 2003 Primary InterOp Assemblies also. Why should
this happen in only one users desktop when we have this add-in running on
100 of other workstation ?

Microsoft.Office.Interop.Outlook.Application oApplication = null;

try

{

comboBox_Folder.Items.Clear();

Type oType = Type.GetTypeFromProgID("Outlook.Application");

if (oType != null)

oApplication =
(Microsoft.Office.Interop.Outlook.Application)Acti vator.CreateInstance(oType);



Unable to cast object of type 'System.__ComObject' to type
'Microsoft.Office.Interop.Outlook.ApplicationClass '.
at
System.Runtime.Remoting.RemotingServices.AllocateU ninitializedObject(RuntimeType
objectType)
at
System.Runtime.Remoting.RemotingServices.AllocateU ninitializedObject(Type
objectType)
at
System.Runtime.Remoting.Activation.ActivationServi ces.CreateInstance(Type
serverType)
at
System.Runtime.Remoting.Activation.ActivationServi ces.IsCurrentContextOK(Type
serverType, Object[] props, Boolean bNewObj)
at System.RuntimeTypeHandle.CreateInstance(RuntimeTyp e type, Boolean
publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle&
ctor, Boolean& bNeedSecurityCheck)
at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean
fillCache)
at System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean
skipVisibilityChecks, Boolean fillCache)
at System.Activator.CreateInstance(Type type, Boolean nonPublic)

TIA
John