Strange Error on finnal step of Checkout process

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>> Version:2,5004
>> URL:http://dev.rira.gr/Checkout.aspx
>> Page:
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>> 18/12/2013 12:14:37 πμ
>> 5.55.189.22
>> DESCRIPTION:
System.ArgumentException: Argument 'Length' must be greater or equal to zero.
at Microsoft.VisualBasic.Strings.Left(String str, Int32 Length)
at CkartrisBLL.ExtractHTMLBodyContents(String strHTML)
at CheckoutComplete.Page_Load(Object sender, EventArgs e)
at System.EventHandler.Invoke(Object sender, EventArgs e)
at System.Web.UI.Control.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

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