Blank Neighborhood Screen?

[MaxisManiac]

Something very odd has just happened to my game for no apparent reason. No new downloads, nothing, and it was working fine yesterday. I loaded up my game and found the neighborhood with the UI and everything, just no houses, terrain, nothing. Just a blank, light blue screen. When moving my mouse over the blueness, there were clickable lots available... so now I'm worried. What to do?

[miros]

I'd say start by deleting or renaming Groups.cache (always a good bet) and the thumbnail files.