I have two pendant lights on the same switch. These are the second set as I had the same problem with each light at different times a few months ago and replaced them.
They are low voltage (12V 50W MR16) halogen lights. One of the fixtures has once again started to act up. Sometimes it works and sometimes it doesn't. It doesn't seem to matter if the fixture is hot or cold. There is no problem with the wiring or connections and the bulb is good.
The only thing I can think of is there may be an issue with the transformer. Above the ceiling is the attic. Can the transformer be effected by temperature or humidity changes if there is not enough insulation or moisture barrier around the box?

blackeye, October 2010

one more thing,make sure that you dont overload the trannie with putting the wrong wattage bulb in them

gts, October 2010

there are trannies,and there are trannies.
the cheap ones are a pest as they overheat and the toc(thermal overload )trips,then you have to wait till it cools down before it resets,then you have the electronic units,that wont pass current if a bulb is out in a two or three bulb unit,in all cases you must make sure that you have no insultion around them,leave a clear area,you get what you pay for,as they say.and as for the trannies they fit in light units,say from b,q and such like,waste of time

gts, October 2010

Thanks for the feedback Peccavi.
Each light is on its own transformer.
Contrary to what I had thought in my previous post, the light will only work before the transformer has heated up. Today it worked for a while, then after about an hour it shut off (the other light was still fine). I opened the fixture up at the ceiling and noticed that the transformer was quite warm. I checked all connections again at the light and the switch... still good. I left it open for a while and after it cooled tried the switch and it worked again.
Also did a search for the product to see if there was anyone else having the same problem and found this review.
http://www.homedepot.ca/webapp/wcs/stores/servlet/CatalogSearchResultView?D=912790&Ntt=912790&catalogId=10051&langId=-15&storeId=10051&Dx=mode+matchallpartial&Ntx=mode+matchall&N=0&Ntk=P_PartNumber#BVRRWidgetID
I think I might be returning both fixtures again and buying something new that is not halogen.

blackeye, October 2010

In my experience a transformer either works or it does not work - I have never encountered an intermittent transformer - but I have seen hundreds of intermittent faults caused by poor connections.

You do not say if both lamps are driven from a single transformer or from two. Obviously if from just one transformer and just one lamp plays up then it can not be the transformer.

Despite your assertion that the wiring and connections are good this is where I would look - dismantle, examine and remake every connection even at the transformer. - Consider also that the physical lamp holder may be defective.

I have thrown away all my low voltage halogens and now use 230V strip neons instead - much more reliable.

Good luck...

Peccavi, October 2010