Conditional formatting for 1 cell if there is an error on any cell on the sheet.

[Chypp]

I've been searching but I couldn't find anything about this. Is should be a simple thing but I just can't get it.
I've tried to apply an ISERROR formula to the Conditional formatting for the entire range of cells [=ISERROR(1:1048576)] and although there are errors on the sheet the result is false. I am already using the normal conditional formatting function to highlight the cells with errors in red but the sheet is so large that it would help if I could see a cell (A1) for example if there were any errors on the entire sheet. If I only select the error cell it works, but if I change it with the entire sheet range it doesn't. What am I doing wrong?

[Pepe Le Mokko]

Select the entire sheet (Ctrl+A) and use the following CF rule =ISERROR(A1). Format as required