I realize others have posted about issues with viewing the cart.  I checked those errors first, but I'm getting a slightly different error.  I upgraded the cart this morning to the vesion downloaded yesterday morning (4.31.00) and get this when trying to view the cart.  I've added one item to the cart and then clicked checkout on the mini cart and get a crticial error.  This worked previously.
	A critical error has occurred.
	Unable to cast object of type 'System.Web.UI.WebControls.LinkButton' to type 'System.Web.UI.WebControls.Button'.
	 
	This is in the DNN event log.
	 
	AssemblyVersion: 5.5.1
	PortalID: 12
	PortalName: MY PORTAL (changed)
	UserID: 1
	UserName: USERNAME (changed)
	ActiveTabID: 1830
	ActiveTabName: Product Details
	RawURL: /Store/ProductDetails.aspx
	AbsoluteURL: /Default.aspx
	AbsoluteURLReferrer: http://www.myportal.com/Store/ProductDetails.aspx (changed)
	UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:2.0.1) Gecko/20100101 Firefox/4.0.1
	DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
	ExceptionGUID: 29f9fab1-94e8-4500-ac77-4945078e866e
	InnerException: Unable to cast object of type 'System.Web.UI.WebControls.LinkButton' to type 'System.Web.UI.WebControls.Button'.
	FileName:
	FileLineNumber: 0
	FileColumnNumber: 0
	Method: Smith.DNN.Modules.MiniCart.MiniCart.IbCheckout_Click
	StackTrace:
	Message: DotNetNuke.Services.Exceptions.PageLoadException: Unable to cast object of type 'System.Web.UI.WebControls.LinkButton' to type 'System.Web.UI.WebControls.Button'. ---> System.InvalidCastException: Unable to cast object of type 'System.Web.UI.WebControls.LinkButton' to type 'System.Web.UI.WebControls.Button'. at Smith.DNN.Modules.MiniCart.MiniCart.IbCheckout_Click(Object sender, EventArgs e) at System.Web.UI.WebControls.LinkButton.OnClick(EventArgs e) at System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument) at System.Web.UI.WebControls.LinkButton.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 ---
	Source:
	Server Name: SERVERNAME