Extract Date From Filename

I think I am on the right track, but I am stuck with importing the date from my excel filename. Currently the following code imports all Excel files from the directory into a table in my database. The excel files are saved like "ABC_BNG_GTR_04012008.XLS" The numbers represent the date. I need for the date to be extracted and place in table into the "callDate" field. When I run my code, I continue to get a runtime error 13 - type mismatch. The code stops at the Mid() statement. What am I doing incorrectly? Thanks in advance.

Option Compare Database

Private Sub btnImport_Click()
Dim strFile As String 'Filename
Dim strFileList() As String 'File Array
Dim intFile As Integer 'File Number
Dim filename As String
Dim path As String
Dim TheDate As Date


DoCmd.SetWarnings False
path = "C:UsersChinaboyDesktopData"

'Loop through the folder & build file list
strFile = Dir(path & "*.xls")

While strFile <> ""
'add files to the list
intFile = intFile + 1
ReDim Preserve strFileList(1 To intFile)
strFileList(intFile) = strFile
strFile = Dir()
Wend

'see if any files were found
If intFile = 0 Then
MsgBox "No files found"
Exit Sub
End If

'cycle through the list of files
For intFile = 1 To UBound(strFileList)
filename = path & strFileList(intFile)
DoCmd.TransferSpreadsheet acImport, acSpreadsheetTypeExcel8, "sheet2", filename, False

'Inserts date in date column based on file name

TheDate = Mid(strFile, 12, 8)

CurrentDb.Execute "UPDATE sheet2 SET callDate =" & "'" & TheDate & "' where callDate is null"


Next intFile

DoCmd.SetWarnings True

End Sub