We upgraded our dnn to 7.3.1 (from 7.1.1) and we are having issues:

- We cant add a new portal anymore, we got "Add New Site is currently unavailable" message in the Firebug console. The full message:

Uncaught Sys.WebForms.PageRequestManagerServerErrorException: Sys.WebForms.PageRequestManagerServerErrorException: Error: Add New Site is currently unavailable. jquery.js:9597
Error.create jquery.js:9597
Sys.WebForms.PageRequestManager._createPageRequestManagerServerError jquery.js:9597
Sys.WebForms.PageRequestManager._parseDelta jquery.js:9597
Sys.WebForms.PageRequestManager._onFormSubmitCompleted jquery.js:9597
(anonymous function) jquery.js:9597
(anonymous function) jquery.js:9597
Sys.Net.WebRequest.completed jquery.js:9597
_onReadyStateChange

- The 'Edit Content' window for HTML modules comes as blank randomly. Our client reported this, don't have all the details yet.

PS: Is there a way to turn off 'Lazy load' feature in the module list? 

I was using latest Chrome (36.0.1985). I just tried with IE 10.0.18 and Firefox 31.0 and still getting same results.

I got better error messages this time:
Sys.WebForms.PageRequestManagerServerErrorException: Error: Add New Site is currently unavailable.
45|error|500|Error: Add New Site is currently unavailable.|

This is what I have in the event viewer:

System.Exception: Unhandled Error:  ---> DotNetNuke.Services.Exceptions.PageLoadException: Error: Add New Site is currently unavailable. ---> DotNetNuke.Services.Exceptions.PageLoadException: Error: Add New Site is currently unavailable. ---> DotNetNuke.Services.Exceptions.ModuleLoadException: Error: Add New Site is currently unavailable. ---> System.Xml.XmlException: Unexpected end of file has occurred. The following elements are not closed: module, modules, pane, panes, tab, tabs, portal. Line 1186, position 14.
   at System.Xml.XmlTextReaderImpl.Throw(String res, String arg)
   at System.Xml.XmlTextReaderImpl.ParseElementContent()
   at System.Xml.XmlCharCheckingReader.Read()
   at System.Xml.XsdValidatingReader.Read()
   at DotNetNuke.Common.XmlValidatorBase.IsValid()
   at DotNetNuke.Modules.Admin.Portals.Signup.cmdUpdate_Click(Object sender, EventArgs e) in f:\web_sites\Microsites\DesktopModules\Admin\Portals\Signup.ascx.cs:line 296
   --- End of inner exception stack trace ---
   at DotNetNuke.Services.Exceptions.Exceptions.ProcessModuleLoadException(String FriendlyMessage, Control ctrl, Exception exc, Boolean DisplayErrorMessage)
   --- End of inner exception stack trace ---
   at DotNetNuke.Services.Exceptions.Exceptions.ProcessPageLoadException(Exception exc, String URL)
   at DotNetNuke.Services.Exceptions.Exceptions.ProcessModuleLoadException(String FriendlyMessage, Control ctrl, Exception exc, Boolean DisplayErrorMessage)
   at DotNetNuke.Modules.Admin.Portals.Signup.cmdUpdate_Click(Object sender, EventArgs e) in f:\web_sites\Microsites\DesktopModules\Admin\Portals\Signup.ascx.cs:line 546
   at System.Web.UI.WebControls.LinkButton.RaisePostBackEvent(String eventArgument)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   --- End of inner exception stack trace ---
   at DotNetNuke.Services.Exceptions.Exceptions.ProcessPageLoadException(Exception exc, String URL)
   at DotNetNuke.Framework.PageBase. (EventArgs e)
   at System.Web.UI.Page.HandleError(Exception e)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest()
   at System.Web.UI.Page.ProcessRequest(HttpContext context)
   at ASP.default_aspx.ProcessRequest(HttpContext context) in c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\fdcf9cd1\837bb063\App_Web_ebhvm2lc.3.cs:line 0
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
   --- End of inner exception stack trace ---