On Jun 8, 3:56*pm, joeu2004 wrote:
With Conditional Formatting, you can highlight the error
[...]. For example, if only one of B1 and B2 should be
non-empty, select B1 and B2, and enter the following CF for
both:
Formula Is: *=AND(ISBLANK($B$1)=FALSE,ISBLANK($B$2)=FALSE)

Arguably easier to write and equivalent:

Formula Is: =OR(ISBLANK($B$1),ISBLANK($B$2))=FALSE