Consider the following scenario:
You use Microsoft SQL Server 2012 Reporting Services (SSRS 2012) or SQL Server 2014 Reporting Services (SSRS 2014).
You create a data-driven subscription and you use a query to drive the subscription.
The query takes longer than 30 seconds to fully execute.
In this scenario, you cannot create the subscription because the query cannot be validated.
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This issue occurs because of a defect in SQL Server 2012. For data-driven subscriptions, any time-out specified by user is not honored by using the web UI or API calls. This will result in long-running queries timing out when you click Validate or Next in the UI, or validate by using API calls.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.