Tables not accepting "Ruling" settings

[Niels Fanøe]

You wrote:
-> 
->    This happens on some files (chapters) within my book, but 
-> not in others. And within a single file/chapter, it can 
-> happen on some tables, but not others.

Would the tables where this happens possibly be imported from, say, Word? If that is the case, you need to open the Custom Ruling and Shading dialog from within the table, select "From Table" in the Apply Ruling Style list, and hit Apply. This should reapply the true table format on the table.

HTH,

Niels