(SSRS 2008 R2) Deployed report does not display any results

I have a report that includes six drop down controls that are used to define the report's criteria selections. The values in these drop down controls are supplied via queries to my database.

The report displays the results correctly in BIDS, retrieving the data from my database. The report deploys to my Report Server without error. When I access the report from my Report Server, select the same criteria from the data-driven drop down controls, and press the View Report button, however, no results are displayed; the report section is blank. No error message is displayed. I noticed that when I press the View Report button, all of my drop down controls blink momentarily but retain the selected values.

The thread "SSRS 2008 R2 Report Rendering issue on Report Manager" sounded promising, but I can't find the specified log files. The only log files I *can* find are located in C:\Program Files\Microsoft SQL Server\MSRS10_50.MSSQLSERVER\Reporting Services\LogFiles.

Each time I press the View Report button, the following data is written to the current ReportServerService*.log file in the above-mentioned directory:

ui!ReportManager_0-1!818!04/30/2013-23:11:45:: e ERROR: System.Web.HttpException: The URL-encoded form data is not valid. ---> System.InvalidOperationException: Operation is not valid due to the current state of the object.
   at System.Web.HttpValueCollection.ThrowIfMaxHttpCollectionKeysExceeded()
   at System.Web.HttpValueCollection.FillFromEncodedBytes(Byte[] bytes, Encoding encoding)
   at System.Web.HttpRequest.FillInFormCollection()
   --- End of inner exception stack trace ---
   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!1068!04/30/2013-23:11:45:: Call to GetSystemPermissionsAction().
ui!ReportManager_0-1!818!04/30/2013-23:11:45:: e ERROR: HTTP status code --> 500
-------Details--------
System.Web.HttpException: The URL-encoded form data is not valid. ---> System.InvalidOperationException: Operation is not valid due to the current state of the object.

   at System.Web.HttpValueCollection.ThrowIfMaxHttpCollectionKeysExceeded()

   at System.Web.HttpValueCollection.FillFromEncodedBytes(Byte[] bytes, Encoding encoding)

   at System.Web.HttpRequest.FillInFormCollection()

   --- End of inner exception stack trace ---

   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!1068!04/30/2013-23:11:45:: Call to GetSystemPropertiesAction().
ui!ReportManager_0-1!818!04/30/2013-23:11:45:: 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)

Can someone help me interpret these messages? As I said, the report displays the results correctly in BIDS...and the data-driven drop down controls function properly...but the report results do not appear. I re-saved and re-deployed the report, but the results were the same.

Chris