Receiving generic SMP error when accessing Targeted Agent Settings > Download tab (Settings > Agents/Plug-ins > Targeted Agent Settings). 

Error 1:

Failed to process web request.

Exception of type 'System.Web.HttpUnhandledException' was thrown.
   [System.Web.HttpUnhandledException @ System.Web]
   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 Altiris.NS.UI.Controls.PageCachePage.ProcessRequest(HttpContext context)
   at Altiris.NS.UI.AltirisPage.ProcessRequest(HttpContext context)

Field not found: 'PeerDownloadSettings.MaxDownloadBandwidth'.
   [System.MissingFieldException @ Altiris.Web.NS]
   at Altiris.NS.UI.Admin.Configuration.cfgGeneralAgentSettingsDetailsDownloads.LoadPeerDownloadControls(PeerDownloadSettings oPeerDownloadSettings)
   at Altiris.NS.UI.Admin.Configuration.cfgGeneralAgentSettingsDetailsDownloads.LoadSettings()
   at Altiris.NS.UI.Admin.Configuration.cfgGeneralAgentSettingsDetailsDownloads.Page_Load(Object sender, EventArgs e)
   at System.Web.UI.Control.OnLoad(EventArgs e)
   at Altiris.NS.UI.Controls.PageCachePage.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

HTTP [GET]: http://localhost/Altiris/NS/Admin/Configuration/cfgGeneralAgentSettingsDetailsDownloads.aspx?ItemGuid=2e71d179-a31b-43fc-8027-35029ffbdf39

ip: [::1]; languages: [en-US];response: [200 OK]; x-smp-nsversion: [8.0.2298.0];

----------------------------------------------------------------------------
Date: 10/3/2017 10:26:04 AM, Tick Count: 487074250 (5.15:17:54.2500000),  Size: 3.13 KB
Process: w3wp (5940), Thread ID: 95, Module: Altiris.NS.UI.dll
Priority: 1, Source: Altiris.NS.UI.AltirisPage.ProcessRequest
 

Error 2:

HTTP Request failed: /Altiris/NS/Admin/Configuration/cfgGeneralAgentSettingsDetailsDownloads.aspx?ItemGuid=2e71d179-a31b-43fc-8027-35029ffbdf39

Field not found: 'PeerDownloadSettings.MaxDownloadBandwidth'.
   [System.MissingFieldException @ Altiris.Web.NS]
   at Altiris.NS.UI.Admin.Configuration.cfgGeneralAgentSettingsDetailsDownloads.LoadPeerDownloadControls(PeerDownloadSettings oPeerDownloadSettings)
   at Altiris.NS.UI.Admin.Configuration.cfgGeneralAgentSettingsDetailsDownloads.LoadSettings()
   at Altiris.NS.UI.Admin.Configuration.cfgGeneralAgentSettingsDetailsDownloads.Page_Load(Object sender, EventArgs e)
   at System.Web.UI.Control.OnLoad(EventArgs e)
   at Altiris.NS.UI.Controls.PageCachePage.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Exception logged from:
   at Altiris.NS.UI.AltirisWebApplication.ReportApplicationError(System.Web.HttpContext)
   at System.Web.HttpApplication.RaiseOnError()
   at System.Web.HttpApplication.RecordError(Exception)
   at System.Web.HttpApplication+PipelineStepManager.ResumeSteps(Exception)
   at System.Web.HttpApplication.BeginProcessRequestNotification(System.Web.HttpContext, AsyncCallback)
   at System.Web.HttpRuntime.ProcessRequestNotificationPrivate(System.Web.Hosting.IIS7WorkerRequest, System.Web.HttpContext)
   at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr, IntPtr, IntPtr, Int32)
   at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr, IntPtr, IntPtr, Int32)
   at System.Web.Hosting.UnsafeIISMethods.MgdIndicateCompletion(IntPtr, System.Web.RequestNotificationStatus&)
   at System.Web.Hosting.UnsafeIISMethods.MgdIndicateCompletion(IntPtr, System.Web.RequestNotificationStatus&)
   at System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(IntPtr, IntPtr, IntPtr, Int32)
   at System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(IntPtr, IntPtr, IntPtr, Int32)

HTTP [GET]:
http://localhost/Altiris/NS/Admin/Configuration/cfgGeneralAgentSettingsDetailsDownloads.aspx?ItemGuid=2e71d179-a31b-43fc-8027-35029ffbdf39
ip: [::1]; languages: [en-US];response: [200 OK]; x-smp-nsversion: [8.0.2298.0];

----------------------------------------------------------------------------
Date: 10/3/2017 10:26:04 AM, Tick Count: 487074250 (5.15:17:54.2500000), Size: 2.47 KB
Process: w3wp (5940), Thread ID: 95, Module: w3wp.exe
Priority: 1, Source: WebApplication

Either the ITMS 8.0 POST-HF6 files were removed from the system or it didn't install properly.

Run a repair on the current ITMS 8.0 POST-HF6 files installed by running PFInstaller2.exe. If you can't find the respective files, download the most recent one from INFO4241 and install it.