assembly conflict Microsoft.ReportViewer.WebForms

[Startech]

After running a update to published app i get a error :\[code\]Parser Error Message: Could not load file or assembly 'Microsoft.ReportViewer.WebForms, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.\[/code\]Source Error:\[code\] Line 1: <%@ Page Title="" Language="C#" MasterPageFile="~/XXX/Pages/MainMaster.Master" AutoEventWireup="true" Line 2: CodeBehind="Report.aspx.cs" Inherits="xxx.yy.cc.tt.Pages.Reports.Report" %>\[/code\]I haven't updated that to 10.0 -> it should be 9.0 . It is 9 in web.config.. Also it is 9.0 for other apps running in same server. So I wonder, where can it get that request command to search for 10.0 version? As I use Visual Studio 2012 for development, I think it mistakenly did it automatically in some phase. However, as I'm beginner I dont know where to search for that "automatically" modified configuration.