Cheers, I seem to have sorted the problem!! It seems the project file I was opening had somehow become corrupt which was causing the issue, and was causing the same error/issue on other projects if I opened them with the 'corrupt' one still open in the background. I opened other Projects on their own and discovered they worked as normal. So long story short I reverted to an older save of the 'corrupt' project file and re-saved as new, now everything seems to be back to normal!! Phew! Cheers