Recent Posts takes you to OOPS that page cannot be found

PLEASE HELP. When using a widget ‘Recent Posts’ I get a page stating OOPS! Cannot find that page, yet when I use Archive I can see my posts. I have followed the instructions on how to create posts and checked them. I have deleted/deactivated all plug in (in case that was the problem) and I have checked my comment settings allow any comments. Please help.