Symptoms
The FORMAT function can't be executed if it's wrapped inside the common language runtime (CLR) in Microsoft SQL Server 2012 Service Pack 3 (SP3), SQL Server 2014 SP2, or SQL Server 2016. This issue occurs when you set the PERMISSION_SET property to SAFE.
Resolution
The issue was first fixed in the following cumulative updates of SQL Server:
Note This issue also occurs in the earlier versions of SQL Server 2012 (RTM, SP1, SP2), if you encounter this issue in the earlier versions of SQL Server 2012, you have to upgrade to SQL Server 2012 SP3 CU4 to fix the issue.
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. We recommend that you download and install the latest cumulative updates for SQL Server:
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology that Microsoft uses to describe software updates.