Where's my type gone?

Have you ever experienced the following situation? Your InDesign file uses 2 columns, you want to change this into 3 columns, but when you do this, a portion of your type disappears and the red square with an x appears. No "insert break character has been used, no new paragraph, the columns are wide enough to fit the type. There just seems to be no reason why the type doesn't flow on. Here are some possible causes.

1. The No break option has been applied to a word or words. This option ensures that words are never hyphenated and stay together including the spaces before or after the word(s) if they too have been selected.

2. In the hyphenation settings menu "the before last" number has been set too high.