Data Validation using IsNumber and IsBlank

Hi everyone,

I am trying to set up a data validation but it's not working as expected.

There cannot be an entry in cell A1 when cell B1 in not blank, and when cell B1 is blank any entry in cell A1 must be a number.

I entered custom formula =AND(ISNUMBER(A1),ISBLANK(B1)). Cell B1 is blank, but when I enter VOID in cell A1 it accepts it and does not give an error. Is my formula incorrect? What should I enter to accomplish this?

Thank,
Gos-C

I got it solved. Uncheck Ignore Blank.

Thanks,
Gos-C