For some reason I can’t always get dupliverts to work in Blender 2.28 (or 2.27 either. I’d test it more but those are the only versions I’ve got). In some files it will work with meshes and lights, in some only with meshes, and in some it won’t even work. Any ideas what could be wrong?
Goo
What are you parenting the light to?
Some more info, or a blend file would be helpful.
If you are doing the dupliverted spots on an Icosphere for fake GI lighting, make sure you do everything in top view. I have found that works properly all the time.
BgDM
hey!
I have got this issue some times too, in 2.28…but not always, dont know why, but suddenly it worked again, weird !!
I was trying to make a fake GI lighting setup when I noticed the problem. I was parenting a spot light to a UV sphere with 12 segments and 12 rings. I just tried it with an icosphere and doing everything in the top view like BgDM suggested, but it still won’t work. The icosphere and the uvsphere were both 80 times bigger than default. I’ve tried sizing them in and out of edit-mode and it didn’t make a difference. After noticing this problem, I tried dupliverting planes and lights with random models I’ve created. Sometimes I could duplivert lamps and planes, sometimes only planes, and sometimes nothing. It seemed fairly random and it occurs in both blender 2.28 and 2.27. Closing and re-opening the program don’t help. Neither does reseting the computer. The files are a bit big for me to post, but I can post a smaller version with some stuff deleted if you want an actuall .blend file.
Goo
This indeed weird then. I just made a blend file and did the fake GI with an Icosphere and all worked perfectly fine.
I will keep my eye on it though.
BgDM
You said doesn’t work 20 times but not once did you say what it does instead of working. Do you really mean that you take mesh, make it parent of an object (whatever object) then turn on duplivert for the parent nothing happens ?
Jean
That’s right. Nothing happens. It’s as if you weren’t pressing the button. I’ve also tried it with and without the rotation setting next to it. It didn’t effect it at all.
Goo
Are you parenting the light to the mesh, or the mesh to the light? This may be your problem.
Select the light first with RMB, hold SHIFT and then select ther mesh with the RMB. ALT+P to parent.
BgDM
I am most definitly parenting the light to the mesh. I’ve made sure of that. I also tried changing the light from a spot to a lamp, which was working in other files, but it did nothing, i.e. no dupliverted lamps. And I think it’s CTRL+P. ALT+P clears the parent. But of course you know that. 
I’m convinced that it’s a flaw in the file or some other fluke, because I’ve gotten it to work in pretty much every other file.
Goo