In DNN,7 install fresh or upgrade from 6.25 when I try to compose message in "Send to:" filed ehn i start writing user name i get error.

An error occurred while getting suggestions:Internal Server Error

Here is parts of log that I thing that is refferent whit tis error:

2012-12-03 16:39:08,835 [REPORTSERVER][Thread:54][FATAL] DotNetNuke.Web.Common.Internal.DotNetNukeHttpApplication - System.TypeLoadException: Could not load type 'System.Net.Http.HttpMessageInvoker' from assembly 'System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.
<br>   at System.Web.Http.WebHost.HttpControllerHandler.BeginProcessRequest(HttpContextBase httpContextBase, AsyncCallback callback, Object state)
<br>   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
<br>   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
<br>2012-12-03 16:39:35,929 [REPORTSERVER][Thread:50][FATAL] DotNetNuke.Web.Common.Internal.DotNetNukeHttpApplication - System.TypeLoadException: Could not load type 'System.Net.Http.HttpMessageInvoker' from assembly 'System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.
<br>   at System.Web.Http.WebHost.HttpControllerHandler.BeginProcessRequest(HttpContextBase httpContextBase, AsyncCallback callback, Object state)
<br>   at

There is no ASP.NET 4.5 instaled on server at all,
I tought that is minimum required ASP.NET 4.0 for DNN not 4.5.

We have installed a fresh DNN 7.4.1 and upgraded .net framework from 4.0 to 4.5 but it didn't help.

############################################################################################################
GET http://dnn.local/DesktopModules/Inter... 500 Internal Server Error

Response:
{"Message":"An error has occurred. :}

"NetworkError: 500 Internal Server Error - http://dnn.local/DesktopModules/Inter...
###########################################################################################################

Any help full tips would be highly appreciated.

Thanks !