Microsoft SQL Server 2012 Reporting Services (SSRS) may fail to export a report to Excel format if the exported file is larger than 10 megabytes (MB).
If the report is exported to Excel by a subscription and the exported file is larger than 10 MB, SSRS will always fail with IsolatedStorageException.
When you are exporting the reports that are larger than 10 MB to Excel worksheets in Report Manager or in any other clients, a deadlock may occur in the back-end, and the sessions will be time out.
Service pack information for SQL Server 2012
To resolve this problem, obtain the latest service pack for Microsoft SQL Server 2012. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2755533 How to obtain the latest service pack for SQL Server 2012
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.