When adding shipping by weight, I receive the following error:

AssemblyVersion: 5.6.2
PortalID: 0
PortalName: Ellesmere Books
UserID: 1
UserName: host
ActiveTabID: 62
ActiveTabName: Store
RawURL: /Store/ctl/ManageShipping/mid/410.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.ellesmerebooks.co.uk/Store/ctl/ManageShipping/mid/410.aspx
UserAgent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: ec505cb7-52ae-437e-9a59-da0ebf7e7a34
InnerException: Input string was not in a correct format.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: System.Number.StringToNumber
StackTrace:
Message: DotNetNuke.Services.Exceptions.PageLoadException: Input string was not in a correct format. ---> System.FormatException: Input string was not in a correct format. at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal) at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info) at System.Convert.ToInt32(String value) at Smith.DNN.Modules.BuyNow.ManageShipping.btnAddShippingByWeight_Click(Object sender, EventArgs e) at System.Web.UI.WebControls.Button.OnClick(EventArgs e) at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) at System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---
 

Nothing is written to the shipbyweight table.