Only functions and extended stored procedures can be executed from within a function.

Error Message:
Msg 557, Level 16, State 2, Line 2
Only functions and extended stored procedures can be executed from within a function.

Severity level:
16.

Description:
This error message appears when you try to execute a normal stored procedure within a function.

Consequences:
The T-SQL statement can be parsed, but causes the error at runtime.

Resolution:
Error of the Severity level 16 are generated by the user and are corrigible by the user. The statement can not be run this way. You can not call a normal stored procedure within a function.

Versions:
This error message was introduced with SQL Server 2000.

Example(s):
IF OBJECT_ID(‘dbo.p’) IS NOT NULL
    DROP PROCEDURE dbo.p;
GO

CREATE PROCEDURE dbo.p
AS
SELECT 1;
GO

IF OBJECT_ID(‘dbo.f’) IS NOT NULL
    DROP FUNCTION dbo.f;
GO

CREATE FUNCTION dbo.f()
RETURNS int
AS
BEGIN
    EXEC dbo.p;
    RETURN 0;
END
GO

SELECT dbo.f();

Remarks:
In the above example we try to call the procedure dbo.p within the function dbo.f. This raises the error.