You tried to set a bookmark to an invalid string.
This error can occur if you set the Bookmark property to a string that is invalid or was not saved from previously reading a Bookmark property. For example, the following code produces this error:
Sub SetBookmark()
Dim dbs As Database
Dim rstEmployees As Recordset
Dim strPlaceholder As String
Set dbs = OpenDatabase("Northwind.mdb")
Set rstEmployees = _
dbs.OpenRecordset _
("Employees", dbOpenDynaset)
strPlaceholder = "1"
rstEmployees.Bookmark = strPlaceholder ' Not a valid bookmark.
End Sub