There are several dozen complaints in the Google Places Help Forum with business owners trying to update their Google Places data and not being able to.
The error message for all these users reads:
System ErrorWe're sorry, but we are unable to serve your request at this time.
Please try back in a few minutes.
There is a single long thread, plus dozens of other threads about the issue in the blogged it last night.
The issues started sometime yesterday and linger on through today.
Forum discussion at Google Place Help.
Update: According to Google, this is now resolved.