%sThere is no function '%ls:%ls()'

Error Message:
Msg 2395, Level 16, State 1, Line 7
%sThere is no function '%ls:%ls()'

Severity level:
16.

Description:
This error message appears when you try to use an unknown XQuery 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 cannot be run this way. The function you call must be a valid XQuery function. For further information, refer to the link in the error message text.

Versions:
This error message was introduced with SQL Server 2005.

Example(s):
DECLARE @xml xml;
SET @xml = '<Result />';
SELECT
    @xml.query('for $a in(1, 2), $b in(3, 4)
    where
        $a < $b
    return SUM($a + $b)') as XML;

Remarks:
In the above example we try to use the function SUM() in the XQuery. Because XQuery is case-sensitive, this is different from the function sum() and thus the error is raised.