I'm experiencing the same problem on some of my SSRS reports, and it appears to be intermittent.

We have several hundred report subscriptions, the SQL Agent Jobs report success, but I get messages in the SSRS log to this effect:

11/17/2013-02:15:31:: Error processing event 'TimedSubscription', data = fdce1441-883d-409c-8dd6-401ed2c9f331, error = Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerStorageException: An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database. ---> System.Data.SqlClient.SqlException: SQLServerAgent exceeded the allowed timeout for creating the shared job list. The Jobs cannot be enumerated.

I've learned that the enumeration is handled by xp_sqlagent_enum_jobs procedure, which is undocumented. However, I can run the following and I get results very quickly (sub-second):

exec master.dbo.xp_sqlagent_enum_jobs 1, ''

The 2 reports that have this issue have been running fine, and nothing has changed for these reports or the servers/etc involved in months. Also, scheduled reports before and after these ran fine. It seems like something else is causing these to hang. Both reports with the issue run outside of business hours when db usage is very low.

Any thoughts? Running on Windows 2008 R2, SQL Server 2012, VMWare esxi 5