Please check this https://social.msdn.microsoft.com/Forums/officeapps/en-US/a347ab0a-ef2e-464a-a914-9a5c2cd7d08e/tryconvert-is-not-a-recognized-builtin-function-name?forum=transactsql

Hello everyone,

I have exactly the same error ([LFF502-UnexpectedError]) when I try to access the “Data Maintenance” page.

In my case, on MSSQL, the compatibility level of the LF_Forms database was at level 100.

Here's the SQL code to display the levels of all your databases.

SELECT name AS DatabaseName, compatibility_level 
FROM sys.databases;

After setting it to level 120, everything went back to normal.

Here's the SQL code to change the level. (remember to indicate the name of your database)

ALTER DATABASE LFForm SET COMPATIBILITY_LEVEL = 120;

I hope I've provided you with some additional information.