Extraneous paren, probably my fault...

=SUM(IF(Year($Z$5:$Z$2050)=AS2,IF(ISNUMBER($V$5:$V $2050),$V$5:$V$2050)))

followed by control+shift+enter.

Pierre wrote:
I translated that into :
=SUM(IF(Year($Z$5:$Z$2050)=AS2),IF(ISNUMBER($V$5:$ V$2050),$V$5:$V$2050)))

It stops and blinks at the entry AS2, and displays a get help with the
formula message.
(in AS2, I've got a 4 digit date: 1999)
Column Z are the dates
Column V are the prices
Once more with feeling.
Thanks for your interest.

Pierre