Exporting an SSRS report to Excel failure

Some other places you could check are:

SSRS Log:

c$\Program Files\Microsoft SQL Server\MSRS11.MSSQLSERVER\Reporting Services\LogFiles

You could try enabling verbose logging (level 4) here

C:\Program Files\Microsoft SQL Server\MSRS11.MSSQLSERVER\Reporting Services\ReportServer\bin\ReportingServicesService.exe.config

Look for this tag:

<switches>
  <add name="DefaultTraceSwitch" value="4" />
</switches>

I'm fighting very similar issue but to make it a bit complex, my subscription fails only every other time or so and runs fine sometimes. So far I ruled out:

• No. of parallel SSRS sessions
• Memory pressure on DB server & Report
• Server Kicking off the subscription directly vs remotely(running
  the agent job)

Sorry, I do not have a good answer for you but this issue seems to bother more than few people.

Update: I found out that the Subscription was a created by a windows user who is no longer valid (ID expired). Updating the Subscription owner fixed it.

-- List SSRS users (check to make sure the new Owner exists in this list)

SELECT *
FROM Users
WHERE UserName IN ('DomainName\_SSRSServiceAccount') 

-- DFGRYH-DFGRYH--DFGRYH-DFGRYH

-- Identify the subscription whose ownership you would like to edit

SELECT *
FROM Subscriptions
WHERE OwnerID = 'DFGRYH-DFGRYH--DFGRYH-DFGRYH'
    AND Description = 'Send e-mail to RichG@DomainName.com'
ORDER BY LastRunTime
    ,LastStatus

-- Update the Subscription with new Owner, the change should reflect on the SSRS reports

UPDATE Subscriptions
SET OwnerID = 'DFGRYH-DFGRYH--DFGRYH-DFGRYH'
WHERE SubscriptionID = 'B33A78FC-933D-47DB-AB50-43D36B24C0B8'

Check your error log for details

c$\Program Files\Microsoft SQL Server\MSRS11.MSSQLSERVER\Reporting Services\LogFiles

Typically this happens when the user who owns the subscription (usually the one who set it up) is no longer a valid user or disabled etc. Try dropping & recreating the sub to isolate bad user case.