Arduino 2560 failing to compile. Will not compile or run any programme. Have been using ok for ages and has suddenly stopped working. Cannot compile or run simple blink prgramme any more. Help!! I get this message when the compiler fails..... C:\Users\bernieaw\Desktop\arduino-1.0.4-windows\arduino-1.0.4\hardware\tools\avr\bin\avr-ar: unable to rename 'core.a'; reason: Permission denied. Any clues please.