We apologize for the inconvenience, but we are unable to process your request at this time. Our engineers have been notified of this problem and will work to resolve it. Please note that using your browser's back button in AdWords can increase the likelihood of errors. If you think this was the cause of your error, please try again without using the back button.
I am not using the back button, is there a limit to how many campains you can start on one day or are they just having problems?
My guess is that this would have been a temporary problem, and that trying again in 10 minutes would have 'fixed' it.
Also, I have learned over time that re-booting my computer seems to resolve about 95% of all issues. It is almost like magic or something. So I would suggest a re-boot, should this happen again. At the very least, try a new browser window.
So it is something in the cache that gets me this error.