Run-time error -2147024809 (80070057)

I get the preceding error message when trying to open a specific report. below is the VB code with the highlighted (problem) text;

Private Sub cmdOpenReport_Click()
Dim stDocName As String
astrParams (0) = "'" & Me.cboAirspace & "'"

stDocName = "rptActsSpecial"
DoCmd.OpenReport stDocName, acViewPreview
Me.Visible = FALSE

End Sub

Any Ideas?