Update error using DataFormatString

[David C]

I have a textbox (see below) that shows the data column from SqlDataSource
as currency.

<asp:TextBox ID="txtSalePrice" runat="server" Text='<%# Bind("SalePrice",
"{0:c}") %>' Width="125px"></asp:TextBox>


However, when I issue the UPDATE command it throws the exception error
below. How can I get around this?
Source: mscorlib

An unhandled exception occurred:

Message: Input string was not in a correct format.



David