Check For Duplicate Data Before Importing

Hello All,

I have a database where a user imports data into a table monthly. She saves the Excel file and then clicks a button in Access to import the data. My instructions say to only click that button once, but so far, she has clicked it THREE TIMES, thus importing the data three times. How can I prevent this? Here is a copy of my import code:

Option Compare Database
Option Explicit

Public Function ImportTableData()
On Error GoTo ImportTableData_Err

Dim strPeriod1 As String
Dim strMM1 As String
Dim strYY1 As String
Dim strYYYY As String
Dim strFormName As String
Dim strMDPath As String
Dim strMDFileName As String
Dim strDCPath As String
Dim strDCFileName As String


'No Warnings
DoCmd.SetWarnings False

'Import Current Month data in a temporary table
DoCmd.OpenForm "frmEnterAgingDates", , , , acFormReadOnly, acHidden
strFormName = "Forms!frmEnterAgingDates"
strPeriod1 = Forms!frmEnterAgingDates.Period1.Value
strPeriod1 = Format(strPeriod1, "mmddyyyy")
strMM1 = Left(strPeriod1, 2)
strYY1 = Right(strPeriod1, 2)
strYYYY = Right(strPeriod1, 4)
strMDPath = "S:FinanceAccounting OperationsNational AccountsAccount Recs116405.100 and 117630.300116405.100-AR Due from PAR Plans NASCO"
strMDFileName = "MD AR Due from PAR Plans_" & strMM1 & strYY1 & ".xls"
strDCPath = "S:FinanceAccounting OperationsNational AccountsAccount Recs116405.100 and 117630.300117630.300-AR NASCO Refund Due from PAR Plans117630-2007"
strDCFileName = "DC AR Due from PAR Plans_" & strMM1 & strYY1 & ".xls"

DoCmd.TransferSpreadsheet , acSpreadsheetTypeExcel9, "tblData_temp", strMDPath & strMDFileName, True
DoCmd.TransferSpreadsheet , acSpreadsheetTypeExcel9, "tblData_temp", strDCPath & strDCFileName, True

'Append tblData_temp to tblData
DoCmd.OpenQuery "qryAppend_tblData_temp_to_tblData", acViewNormal, acEdit

'Delete any blank rows that may have resulted from the import
DoCmd.OpenQuery "qryDeleteBlankRows", acViewNormal, acEdit

'Delete the temporary table
DoCmd.OpenQuery "qryDelete_tblData_temp"

Beep
MsgBox "The file has been successfully imported", vbInformation, "Files Imported"

ImportTableData_Exit:
Exit Function

ImportTableData_Err:
MsgBox Error$
Resume ImportTableData_Exit


End Function

Thank you for your help!