I had a customer purchase a product today and this was in the event viewer.

UserAgent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; InfoPath.1; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 90db09a3-0458-42a0-a3a7-77c158b3a034
InnerException: Object reference not set to an instance of an object.
FileName: 
FileLineNumber: 0

FileColumnNumber: 0

Method: Smith.DNN.Modules.BuyNow.ConfirmStatus.ClearCartItems
StackTrace: 
Message: DotNetNuke.Services.Exceptions.PageLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at Smith.DNN.Modules.BuyNow.ConfirmStatus.ClearCartItems() at Smith.DNN.Modules.BuyNow.ConfirmStatus.Redirect() at Smith.DNN.Modules.BuyNow.ConfirmStatus.btnSubmit_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 --

The purchase was successful thankfully.