I've had a demo site up for about 3 weeks for people to look at and it's been running fine.
Last night it started delivering blank pages on a contact form page and on the admin page (which were working fine yesterday afternoon).
After reading here, I tried to delete the .js files in _combined files, but I don't have permissions on them to delete them. So I simply renamed the _combinedfiles folder (which I did have permissions on) and all is working again.
What on earth could have caused that to happen suddenly and how can I avoid it in the future?
Okay, I could deactivate combined files in the config file, but turning off useful functions to make the system work is not the point of the exercise.