Thank you.
That solved the problem.
I assume that I previously inadvertently marked and deleted the tag, when removing an underlying asterisk, after cutting and pasting source references into the Biography area <ref>...</ref> statements. Sometimes, marking text with a mouse, gets additional text that is not wanted to be marked, also marked, and subsequently cut or deleted.
Problem is now solved, and, I need to be even more careful, when marking text with a mouse.