Why does this Friday 13th program fail?

[jebem]

Thank you for sharing this neat program, Joe.

I quit programming long time ago (because I don't need it for my work anymore), so when I looked to the first program listing I couldn't immediately see anything wrong, but the two consecutive END statements following a RETURN did call my attention to check the begin-end code blocks in more detail.

I didn't try the program myself, but my understanding is that the Prime interpreter will not detect any anomalies in the first code listing, meaning that from the point of syntax correctness the Prime will find no errors.

It seems that in the first posted algorithm, the FOR loop was interrupted due to an early exit imposed by the RETURN statement, right?