System.IO.IsolatedStorage.IsolatedStorageException: Unable to create mutex

I get the following error when trying to export output to an excel spreadsheet on my website. The funny thing is, it works for a while, about a day or two, but then starts timing out and throwing this error. We've already messed with the timeouts and that didn't work. In order to work around the error, I go into the apppool and change its identity. Whenever I change the identity of the apppool, it works all of a sudden, but then, it fails again in a day or two and throws the same error. Again, it starts to work but will eventually break again and throw the error. At first, the apppool was using Network Service as the Identity, then Local System, then Local Service. I just cycle through each as a workaround to the issue. Does anyone have any idea how to resolve this error, instead of having to monitor it constantly and keep switching the identity? I am using Windows 2008, IIS 7.5, and ASP.NET 4.0. Here is the error output:

System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.IO.IsolatedStorage.IsolatedStorageException: Unable to create mutex. (Exception from HRESULT: 0x80131464)
   at System.IO.IsolatedStorage.IsolatedStorageFile.Open(String infoFile, String syncName)
   at System.IO.IsolatedStorage.IsolatedStorageFile.Lock(Boolean& locked)
   at System.IO.IsolatedStorage.IsolatedStorageFileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, IsolatedStorageFile isf)
   at System.IO.IsolatedStorage.IsolatedStorageFileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, IsolatedStorageFile isf)
   at MS.Internal.IO.Packaging.PackagingUtilities.SafeIsolatedStorageFileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, ReliableIsolatedStorageFileFolder folder)
   at MS.Internal.IO.Packaging.PackagingUtilities.CreateUserScopedIsolatedStorageFileStreamWithRandomName(Int32 retryCount, String& fileName)
   at MS.Internal.IO.Packaging.SparseMemoryStream.EnsureIsolatedStoreStream()
   at MS.Internal.IO.Packaging.SparseMemoryStream.SwitchModeIfNecessary()
   at MS.Internal.IO.Packaging.CompressEmulationStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at MS.Internal.IO.Packaging.CompressStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at MS.Internal.IO.Zip.ProgressiveCrcCalculatingStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at MS.Internal.IO.Zip.ZipIOModeEnforcingStream.Write(Byte[] buffer, Int32 offset, Int32 count)
   at System.IO.StreamWriter.Flush(Boolean flushStream, Boolean flushEncoder)
   at System.IO.StreamWriter.Write(String value)
   at OfficeOpenXml.ExcelWorksheet.UpdateRowCellData(StreamWriter sw)
   at OfficeOpenXml.ExcelWorksheet.SaveXml()
   at OfficeOpenXml.ExcelWorksheet.Save()
   at OfficeOpenXml.ExcelWorkbook.Save()
   at OfficeOpenXml.ExcelPackage.GetAsByteArray(Boolean save)
   at OfficeOpenXml.ExcelPackage.GetAsByteArray()
   at EDW.QuickHits.Excel.Page_Load(Object sender, EventArgs e) in E:\devedw\QuickHits\Excel.aspx.cs:line 86
   at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   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 ASP.quickhits_excel_aspx.ProcessRequest(HttpContext context) in c:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files\root\ed8a505e\e628d3dd\App_Web_ki0glgcu.5.cs:line 0
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)