i can't get error by using this code.
Try this code!!
just modify onclick event of button.
aspx:
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="FileUpload1"
ErrorMessage="File Required!">
</asp:RequiredFieldValidator>
<br />
<asp:Button ID="Button1" runat="server" Text="Upload" onclick="Button1_Click" />
<asp:Label ID="newlbl" runat="server"></asp:Label>
aspx.cs:
protected void Button1_Click(object sender, EventArgs e)
{
if (FileUpload1.HasFile)
{
newlbl.Text = FileUpload1.PostedFile.FileName;
}
}