EXCEL2007 sqrt() BUG found!!! Can an experienced user verify this?

I was doing college work and had to enter some formulas.
I've seen this weird error resulting from sqrt() function.
It's gotta be a bug. Can someone tell me if it's EXCEL issue or my personal failure???

Location: On sheet 2, on the 69th row, column E.
It gives me a Num! error. It can't be, because the answer inside the sqrt() is Zero, so the answer is 0.

Thank you!