Inaccessible areas in Writer doc

Occasionally I get blank lines (areas) in a Writer doc that cannot be removed or text entered into using the usual delete/backspace key commands. How can these be removed?

Do you handle native odt files or do you edit Word files (doc, docx, …)? If it is the second one so there may be some irregular appearances…

To make it clearer upload a sample file to examine on my (or of somebody else’s) dissecting table.