#VALUE! Error while trying to use a referencing cell in a formula

I would like to use the value inside a cell which continuously gets updated from a web page. The cell called C21 linked to another sheet called 'ratedatasheet'and that sheet displays a page and table from a site online.

I want to use the value inside C21 (linked as RATEDATASHEET.A79) in a formula such as this one: =IF(E24=0;A24*C20;A24*C24)

This formula is placed in B24 cell and, all I am getting as a result is #VALUE! error. I tried like removing the letters from the source cell but it did not help.

What am I doing wrong? Thanks