Under the Opera tab go to preferences
Choose the Privacy & Security menu from the left hand side.
Click on "clear browsing data"
You will be given an option list of things to clear, the only one you need to clear is "cached imagers and files" so check that one and uncheck all the rest.
You get an option to "obliterate the following items for" - the past hour, the past day, the past week, the past four weeks and all time.
Choose the suitable one for you (past day or week, is probably enough) and click on the "clear browsing data" box.

A bit of grinding of gears will follow and then all should be right in the world!

Cheers