Identifier prod undefined

I have calculated the time-weighted return for different periods using the code below for several years.

type _SECTION_BEGIN("Time-Weighted Return");
// This formula calculates the time-weighted return for different periods.

// Calculate the 5 day time-weighted return
twr5 = Prod( C, 5 ) - 1;

// Calculate the 21 day time-weighted return
twr21 = Prod( C, 21 ) - 1;

// Calculate the 63 day time-weighted return
twr63 = Prod( C, 63 ) - 1;

// Exploration
Filter = 1;

AddColumn( C, "TWR", 1.5 );
AddColumn( twr5, "5-Day TWR", 1.5 );
AddColumn( twr21, "21-Day TWR", 1.5 );
AddColumn( twr63, "63-Day TWR", 1.5 );

_SECTION_END();or paste code here

Recently, I had to reinstall Amibroker on my computer due to a hard drive issue. I ran the code below for the first time and got an error that the identifier 'prod' is undefined and the operation is not allowed.

I double checked the Amibroker function reference guide and seem to be using the 'prod' function correctly.

Why am I getting this error when I have never gotten it before?

You need minimum AmiBroker 6.20.
It is clearly mentioned on the webpage of your picture on top right corner (if you would have included it in your picture)
So watch again
And then check your installed AmiBroker version.