Ok, copy this revised method over and let me know how it goes.

Private Sub cmdCloseSplash_Click()
On Error GoTo Err_cmdCloseSplash_Click

       Dim stDocName As String

       DoCmd.Close acForm, "frmMain"
   
   'Expiry Check takes a while, display form while waiting
       DoCmd.OpenForm "frmExpiryStatus"
             
   'Expiry Check
       stDocName = "rptExpiry"
   
       If CurrentProject.AllForms("frmExpiryStatus").IsLoaded = True Then
           If IsNull(DLookup("strDispositionNumber", "qryExpiry")) Then
               MsgBox "Expiry Check OK. Preview cancelled", vbInformation
           Else
               DoCmd.OpenReport stDocName, acViewPreview
               DoCmd.Maximize
               DoCmd.Close acForm, "frmExpiryStatus"
               MsgBox "Pending Expiration Dates require your attention",
vbInformation
           End If
       End If
   
Exit_cmdCloseSplash_Click:
   Exit Sub

Err_cmdCloseSplash_Click:
   Dim errorMessage As String
   errorMessage = "An error has occurred while attempting to view the
Expiry Status report" & Chr(13) & Chr(13)
   errorMessage = errorMessage & Err.Number & ": " & Err.Description
   MsgBox errorMessage, vbOKOnly + vbCritical, "Error Message"
   Resume Exit_cmdCloseSplash_Click

End Sub

One final suggestion... I usually create a separate class for this kind of
thing.  Usually consists of a dedicated progress screen that either shows a
progress bar or an animated GIF showing the operation being carried out.  The
form usually has a label or two that I can pass strings into as well so I can
display custom messages.  Just a thought for your consideration.

Lance