I keep receiving this on one of my DNN sites after upgrading to DNN 5.5.1:

AssemblyVersion: 5.5.1
PortalID: 10
PortalName: ###########################
UserID: -1
UserName: 
ActiveTabID: 487
ActiveTabName: Home
RawURL: /
AbsoluteURL: /default.aspx
AbsoluteURLReferrer: 
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.3 (KHTML, like Gecko) Chrome/6.0.472.63 Safari/534.3
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 1f9e2ad6-53e4-4a7b-802f-506f72400e88
InnerException: The string parameter 'tagPrefix' cannot be null or empty. Parameter name: tagPrefix
FileName: 
FileLineNumber: 0
FileColumnNumber: 0
Method: System.Web.UI.TagPrefixAttribute..ctor
StackTrace: 
Message: DotNetNuke.Services.Exceptions.PageLoadException: The string parameter 'tagPrefix' cannot be null or empty. Parameter name: tagPrefix ---> System.ArgumentException: The string parameter 'tagPrefix' cannot be null or empty. Parameter name: tagPrefix at System.Web.UI.TagPrefixAttribute..ctor(String namespaceName, String tagPrefix) at System.Reflection.CustomAttribute._CreateCaObject(RuntimeModule pModule, IRuntimeMethodInfo pCtor, Byte** ppBlob, Byte* pEndBlob, Int32* pcNamedArgs) at System.Reflection.CustomAttribute.CreateCaObject(RuntimeModule module, IRuntimeMethodInfo ctor, IntPtr& blob, IntPtr blobEnd, Int32& namedArgs) at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean mustBeInheritable, IList derivedAttributes, Boolean isDecoratedTargetSecurityTransparent) at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeAssembly assembly, RuntimeType caType) at System.Web.UI.AssemblyCache.GetAjaxFrameworkAssemblyAttribute(Assembly assembly) at System.Web.UI.ScriptManager.get_DefaultAjaxFrameworkAssembly() at System.Web.UI.ScriptManager..ctor() at DotNetNuke.Framework.AJAX.AddScriptManager(Page objPage) at DotNetNuke.Framework.PageBase.OnInit(EventArgs e) at System.Web.UI.Control.InitRecursive(Control namingContainer) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---

I suspect it has something to do with my skin file, here are my tags in my skin file:
<%@ Control language="vb" AutoEventWireup="false" Explicit="True" Inherits="DotNetNuke.UI.Skins.Skin" %>
<%@ Register TagPrefix="dnn" TagName="SEARCH" Src="~/Admin/Skins/Search.ascx" %>
<%@ Register TagPrefix="dnn" TagName="LOGO" Src="~/Admin/Skins/Logo.ascx" %>
<%@ Register TagPrefix="dnn" TagName="BREADCRUMB" Src="~/Admin/Skins/BreadCrumb.ascx" %>
<%@ Register TagPrefix="dnn" TagName="LOGIN" Src="~/Admin/Skins/Login.ascx" %>
<%@ Register TagPrefix="dnn" TagName="USER" Src="~/Admin/Skins/User.ascx" %>
<%@ Register TagPrefix="dnn" TagName="COPYRIGHT" Src="~/Admin/Skins/Copyright.ascx" %>
<%@ Register TagPrefix="dnn" TagName="PRIVACY" Src="~/Admin/Skins/Privacy.ascx" %>
<%@ Register TagPrefix="dnn" TagName="TERMS" Src="~/Admin/Skins/Terms.ascx" %>
<%@ Register TagPrefix="dnn" TagName="STYLES" Src="~/Admin/Skins/Styles.ascx" %>
<%@ Register TagPrefix="dnn" TagName="NAV" Src="~/Admin/Skins/Nav.ascx" %>

Thanks, I was in denial that I had ever utilized the gallery module.  The old BIN files were lingering in the directly from several years before. 
Surprised the gallery BIN files didn't get deleted after previous uninstall?