Multiselect drop down causing subscription issue

I am trying to create a subscription for a report with a very large multi-select drop down - about 1500 drop down items equaling over 13,000 characters.  When I only select a few of the options from the drop down I am able to create the SSRS subscription just fine.  However when I select all, I get the following error:

"Operation is not valid due to the current state of the object."

Here is the error I sometimes get in the log file:
ui!ReportManager_0-1!a88!12/23/2014-10:35:22:: e ERROR: System.InvalidOperationException: Operation is not valid due to the current state of the object.
   at System.Web.HttpRequest.FillInFormCollection()
   at System.Web.HttpRequest.get_Form()
   at System.Web.HttpRequest.get_HasForm()
   at System.Web.UI.Page.GetCollectionBasedOnMethod(Boolean dontReturnNull)
   at System.Web.UI.Page.DeterminePostBackMode()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
library!ReportServer_0-2!61c!12/23/2014-10:35:22:: i INFO: Call to GetSystemPermissionsAction().
ui!ReportManager_0-1!a88!12/23/2014-10:35:22:: e ERROR: HTTP status code --> 500
-------Details--------
System.InvalidOperationException: Operation is not valid due to the current state of the object.

   at System.Web.HttpRequest.FillInFormCollection()

   at System.Web.HttpRequest.get_Form()

   at System.Web.HttpRequest.get_HasForm()

   at System.Web.UI.Page.GetCollectionBasedOnMethod(Boolean dontReturnNull)

   at System.Web.UI.Page.DeterminePostBackMode()

   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
library!ReportServer_0-2!61c!12/23/2014-10:35:22:: i INFO: Call to GetSystemPropertiesAction().
ui!ReportManager_0-1!a88!12/23/2014-10:35:22:: e ERROR: System.Threading.ThreadAbortException: Thread was being aborted.
   at System.Threading.Thread.AbortInternal()
   at System.Threading.Thread.Abort(Object stateInfo)
   at System.Web.HttpResponse.End()
   at Microsoft.ReportingServices.UI.ReportingPage.ShowErrorPage(String errMsg)

Related fixes regarding this error can be found in these MS posts:
https://social.msdn.microsoft.com/Forums/sqlserver/en-US/cb6ede72-6ed1-4379-9d3c-847c11b75b32/report-manager-operation-cannot-run-due-to-current-state-of-the-object?forum=sqlreportingservices
https://social.msdn.microsoft.com/Forums/sqlserver/en-US/c9d4431a-0d71-4782-8f38-4fb4d5b7a829/ssrs-operation-is-not-valid-due-to-the-current-state-of-the-object?forum=sqlreportingservices

I added the following lines to my web.config file and tried several large numbers for the value:
<appSettings>
 <add key="aspnet:MaxHttpCollectionKeys" value="999000" />
</appSettings>

This did nothing to resolve the issue.

I would appreciated any feedback, or assistance with this issue.