Google Analytics data not being collected correctly

I've been using Google Analytics for quite a while, but from May 29th, data for all except one of my subsites stopped working. They are reported as zero (except for that one site).

I thought there might just have been a drop in traffic due to search engine issues, but the logs of contact form submissions confirms that people are still coming.

I'm stumped. Can't figure out why this would have happened.

Help please.