sendobject isn't available now

[Mark]

Out of 9 computers running access xp, 2 of them give me the error :"The
command or action 'SendObject' isn't available now".

I am using the sendobject to do a simple email of a report. Here is the code.
Private Sub Send_Email_Confirmation_Click()
On Error GoTo Err_Send_Email_Confirmation_Click

Dim stDocName As String
Dim stName As String
Dim stsubject As String
Dim stmessage As String
Dim stm1 As String
Dim stm2 As String
Dim stm3 As String
Dim sthtml As String
Dim stcamper As String

stm1 = [Dear]
stcamper = [CamperSbFrm]![FirstName]
stDocName = "NewReceiptRpt"
stName =
stsubject = "Your 2007 Confirmation!"
stmessage = "Dear " + stm1 + "," + Chr$(13) + Chr$(10) + Chr$(13) +
Chr$(10) + "Your 2007 Summer Camp Confirmation for " + stcamper + " is
attached." + Chr$(13) + Chr$(10) + "Please review for any corrections needed.
" + Chr$(13) + Chr$(10) + Chr$(13) + Chr$(10) + " If you have questions
concerning your application, please call, " + Chr$(13) + Chr$(10) + "Tricia
800-711-4729"
DoCmd.SendObject acReport, stDocName, acFormatHTML, stName, , ,
stsubject, stmessage

Exit_Send_Email_Confirmation_Click:
Exit Sub

Err_Send_Email_Confirmation_Click:
MsgBox Err.Description
Resume Exit_Send_Email_Confirmation_Click

End Sub


I have tried many things, but cannot find a solution.

Mark