We had the same problem, therefore we also distribute a signed otm
file with our VSTO Addins For Outlook.

In the Application_Startup Event of the Application object inside our
otm file,
we check the registry entries for particular addins and if the addin
has been disabled , we change the registry settings correspondingly to
the normal state and force a restart in outlook with Application.Quit
command.

Public Function CheckOutlookAddins(SourceApplication As Application)
Dim csfKey As String
csfKey = RegRead(HKEY_CURRENT_USER, "Software\Nowhere\NoWhereAddin",
"CheckReinstall")
If csfKey = "1" Then
On Error GoTo Cleanup
Set generalApplication = SourceApplication
Dim outlookApplication As Application
Set outlookApplication = SourceApplication
Dim correctionResult As Boolean
Dim addinCount As Integer
Dim foundAddin As COMAddIn
addinCount = outlookApplication.COMAddIns.Count
For i = 1 To addinCount
If outlookApplication.COMAddIns(i).Description = CSFDescription
Then
Set foundAddin = outlookApplication.COMAddIns(i)
If Not foundAddin.Connect Then
On Error Resume Next
foundAddin.Connect = True
If Err.Number 0 Then
Err.Clear
Set foundAddin = Nothing
End If
On Error GoTo Cleanup
Exit For
Else
Exit For
End If
End If
Next

'Everything Running Fine Exit Loop
If foundAddin Is Nothing Then
Dim processResult As CreationStates
processResult = ProcessRegistryKeys()
Select Case processResult
Case CreationStates.CreationSuccess
If Not CheckOutlookAddinsStandalone(SourceApplication,
False) Then
CheckOutlookAddinsStandalone SourceApplication, True
End If
Case CreationStates.DllIsMissing
MsgBox ("Addin Dlls Missing. Registry Key Will Be
Disabled")
RegWrite HKEY_CURRENT_USER, "Software\Nowhere
\NoWhereAddin", "CheckReinstall", "0"
Exit Function
Case Else
GoTo Cleanup
End Select
Else
CorrectAddinStructure SourceApplication, foundAddin
End If

Exit Function

Cleanup:
Set outlookApplication = Nothing
Set generalApplication = Nothing
Set foundAddin = Nothing
MsgBox GetCurrentLanguageFromParameters & Err.Description
End If
End Function

On Jul 21, 11:09*pm, Vidya wrote:
We have an Outlook 2003 addin written in VSTO 2005. We deploy into HKLM so
there is no manual way to disable the addin using Outlook Tools menu. In
production mode, the addin still gets disabled sometimes. We have found out
that one of the ways that user can disable the addin is by killing the
Outlook process while it is still loading. We have implemented ways to make
the addin start up faster and there is not much we can do there.

Are there other ways in which the addin can be disabled? If so, how can we
prevent the addin from being disabled? We implement ThisAddin_Startup and
ThisAddin_Shutdown methods and these are enclosed in try..catch blocks.

Thanks