When I load either of the two portals we have set up, the only thing it says is:

An error has occurred.
An error has occurred.

THAT"S ALL!
However, the URL does show:
http://www.domain.org/Default.aspx?tabid=60&error=Invalid+character+in+the+given+encoding.+Line+1%2c+position+1.&content=0

Does anyone know what that means?  
Nothing seems to have changed on the filesystem for months.  Another user changed some text in an HTML module yesterday.  I looked at that entry in the SQL Server and there's nothing suspicious about it.  She assured me everything was fine when using it yesterday as well. 

In the EventLog database table I'm seeing things like this:

<LogProperties><LogProperty><PropertyName>AssemblyVersion</PropertyName><PropertyValue>04.04.01</PropertyValue></LogProperty><LogProperty><PropertyName>PortalID</PropertyName><PropertyValue>0</PropertyValue></LogProperty><LogProperty><PropertyName>PortalName</PropertyName><PropertyValue>The Murphy Institute</PropertyValue></LogProperty><LogProperty><PropertyName>UserID</PropertyName><PropertyValue>-1</PropertyValue></LogProperty><LogProperty><PropertyName>UserName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>ActiveTabID</PropertyName><PropertyValue>85</PropertyValue></LogProperty><LogProperty><PropertyName>ActiveTabName</PropertyName><PropertyValue>Contact Us</PropertyValue></LogProperty><LogProperty><PropertyName>RawURL</PropertyName><PropertyValue>/Default.aspx?tabid=85&amp;error=Invalid+character+in+the+given+encoding.+Line+1%2C+position+1.&amp;content=0</PropertyValue></LogProperty><LogProperty><PropertyName>AbsoluteURL</PropertyName><PropertyValue>/Default.aspx</PropertyValue></LogProperty><LogProperty><PropertyName>AbsoluteURLReferrer</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>UserAgent</PropertyName><PropertyValue>Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)</PropertyValue></LogProperty><LogProperty><PropertyName>DefaultDataProvider</PropertyName><PropertyValue>DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider</PropertyValue></LogProperty><LogProperty><PropertyName>ExceptionGUID</PropertyName><PropertyValue>d72a0c88-bcfd-4b70-9e78-f849ef478c84</PropertyValue></LogProperty><LogProperty><PropertyName>InnerException</PropertyName><PropertyValue>Invalid character in the given encoding. Line 1, position 1.</PropertyValue></LogProperty><LogProperty><PropertyName>FileName</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>FileLineNumber</PropertyName><PropertyValue>0</PropertyValue></LogProperty><LogProperty><PropertyName>FileColumnNumber</PropertyName><PropertyValue>0</PropertyValue></LogProperty><LogProperty><PropertyName>Method</PropertyName><PropertyValue>System.Xml.XmlTextReaderImpl.Throw</PropertyValue></LogProperty><LogProperty><PropertyName>StackTrace</PropertyName><PropertyValue /></LogProperty><LogProperty><PropertyName>Message</PropertyName><PropertyValue>DotNetNuke.Services.Exceptions.PageLoadException: Invalid character in the given encoding. Line 1, position 1. ---&gt; System.Xml.XmlException: Invalid character in the given encoding. Line 1, position 1.
   at System.Xml.XmlTextReaderImpl.Throw(Exception e)
   at System.Xml.XmlTextReaderImpl.Throw(String res, String arg)
   at System.Xml.XmlTextReaderImpl.InvalidCharRecovery(Int32&amp; bytesCount, Int32&amp; charsCount)
   at System.Xml.XmlTextReaderImpl.GetChars(Int32 maxCharsCount)
   at System.Xml.XmlTextReaderImpl.ReadData()
   at System.Xml.XmlTextReaderImpl.SwitchEncoding(Encoding newEncoding)
   at System.Xml.XmlTextReaderImpl.ParseXmlDeclaration(Boolean isTextDecl)
   at System.Xml.XmlTextReaderImpl.Read()
   at System.Xml.XPath.XPathDocument.LoadFromReader(XmlReader reader, XmlSpace space)
   at System.Xml.XPath.XPathDocument..ctor(Stream stream)
   at DotNetNuke.UI.Utilities.BrowserCaps.GetBrowserCaps()
   at DotNetNuke.UI.Utilities.ClientAPI.BrowserSupportsFunctionality(ClientFunctionality eFunctionality)
   at DotNetNuke.UI.Utilities.DNNClientAPI.EnableMinMax(Control objButton, Control objContent, Int32 intModuleId, Boolean blnDefaultMin, String strMinIconLoc, String strMaxIconLoc, MinMaxPersistanceType ePersistanceType, Int32 intAnimationFrames)
   at DotNetNuke.UI.Containers.Visibility.Page_PreRender(Object sender, EventArgs e)
   at System.Web.UI.Control.OnPreRender(EventArgs e)
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   --- End of inner exception stack trace ---</PropertyValue></LogProperty><LogProperty><PropertyName>Source</PropertyName><PropertyValue /></LogProperty></LogProperties>