Event code: 3005 Event message: An unhandled exception has occurred - asp.net

Question

We have a Asp.net solution (having c# and vb.net code with Ajax). Was running fine in Test and when moved to Prod , it started giving JavaScript errors. And happens for many pages When checked server got the following error.
Event code: 3005
Event message: An unhandled exception has occurred.
Event time: 31/03/2014 13:48:10
Event time (UTC): 31/03/2014 12:48:10
Event ID: 37dd3345a5964cf19ac94b2c05976457
Event sequence: 3
Event occurrence: 1
Event detail code: 0
Application information:
Application domain: /LM/W3SVC/7862/Root-4-130407436897106054
Trust level: Full
Application Virtual Path: /
Application Path: D:\MSINetData\WWW\MT\
Machine name: P01TSDES01
Process information:
Process ID: 28140
Process name: w3wp.exe
Account name: NT AUTHORITY\NETWORK SERVICE
Exception information:
Exception type: MethodAccessException
Exception message: Attempt to access method System.Management.Instrumentation.InstrumentedAttribute..ctor(System.String) in violation of security transparency rules failed.
at System.RuntimeMethodHandle.CheckLinktimeDemands(IRuntimeMethodInfo method, RuntimeModule module, Boolean isDecoratedTargetSecurityTransparent)
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.Reflection.RuntimeAssembly.GetCustomAttributes(Boolean inherit)
at System.Web.UI.AssemblyCache.GetAjaxFrameworkAssemblyAttribute(Assembly assembly)
at System.Web.UI.ScriptManager.get_DefaultAjaxFrameworkAssembly()
at System.Web.UI.ScriptManager..ctor()
at ASP.repository_projectcontact_aspx.__BuildControlToolkitScriptManager1()
at ASP.repository_projectcontact_aspx.__BuildControlContent2(Control __ctrl)
at System.Web.UI.CompiledTemplateBuilder.InstantiateIn(Control container)
at System.Web.UI.MasterPage.InstantiateInContentPlaceHolder(Control contentPlaceHolder, ITemplate template)
at ASP.master_mt_master.__BuildControlMTMContent()
at ASP.master_mt_master.__BuildControlform1()
at ASP.master_mt_master.__BuildControlTree(master_mt_master __ctrl)
at ASP.master_mt_master.FrameworkInitialize()
at System.Web.UI.UserControl.InitializeAsUserControlInternal()
at System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection)
at System.Web.UI.Page.get_Master()
at System.Web.UI.Page.ApplyMasterPage()
at System.Web.UI.Page.PerformPreInit()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
Request information:
Request URL:
Request path: /Repository/ProjectContact.aspx
User host address:
User:
Is authenticated: False
Authentication Type:
Thread account name: P01TSDES01\MX-PAR
Thread information:
Thread ID: 5
Thread account name: P01TSDES01\MX-PAR
Is impersonating: False
Stack trace: at System.RuntimeMethodHandle.CheckLinktimeDemands(IRuntimeMethodInfo method, RuntimeModule module, Boolean isDecoratedTargetSecurityTransparent)
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.Reflection.RuntimeAssembly.GetCustomAttributes(Boolean inherit)
at System.Web.UI.AssemblyCache.GetAjaxFrameworkAssemblyAttribute(Assembly assembly)
at System.Web.UI.ScriptManager.get_DefaultAjaxFrameworkAssembly()
at System.Web.UI.ScriptManager..ctor()
at ASP.repository_projectcontact_aspx.__BuildControlToolkitScriptManager1()
at ASP.repository_projectcontact_aspx.__BuildControlContent2(Control __ctrl)
at System.Web.UI.CompiledTemplateBuilder.InstantiateIn(Control container)
at System.Web.UI.MasterPage.InstantiateInContentPlaceHolder(Control contentPlaceHolder, ITemplate template)
at ASP.master_mt_master.__BuildControlMTMContent()
at ASP.master_mt_master.__BuildControlform1()
at ASP.master_mt_master.__BuildControlTree(master_mt_master __ctrl)
at ASP.master_mt_master.FrameworkInitialize()
at System.Web.UI.UserControl.InitializeAsUserControlInternal()
at System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, IDictionary contentTemplateCollection)
at System.Web.UI.Page.get_Master()
at System.Web.UI.Page.ApplyMasterPage()
at System.Web.UI.Page.PerformPreInit()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
Custom event details:
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Answer 1

Seems like you're having security issue. asp:ScriptManager is a typical cause for this error.
Maybe you should try adding this to your web.config:
<system.web>
<trust level="Full"/>
</system.web>