A week or so there was a bad crash (derailment) near Hua Hin, with various finger pointing, etc. since then there have been various work stoppages, a couple of days of cancellations and most lately stranding of many passengers:

http://www.nationmultimedia.com/sear...ngers+stranded

As far as I can tell this has mainly affected the southern line - but if you are planning to use the trains you might want to check the Thai papers and have alternate plans.