I'm having trouble using special abilities when a card is undimmed. The little star which pops up over the icon on the screen is not appearing.
For example, with Volcanic Phoenix, Alabaster Palace, Fire Beetle I cannot use their abilities at all.
Cards like Nether Plasma or Journeyman Necromancer I can use the ability once the creature is dimmed, but not before.
I've tried this on two different computers in both the client and the broweser version and it is acting the same in all of them. Strangely, it doesn't seem to be affecting my opponent.

Update:
Maybe I am the only player who likes the small interface. On the small interface there is no picture of the selected entity in the Player Status section of the screen. The activation button for special abilities appears on the figure on the playing field or next the enchantment name in the upper right hand corner for world enchantments. The button is no longer appearing.
When I use the large or dynamic interface, the button appears as normal in the little picture of the entity which appears in the player status section. Even better, I can use it.

Would someone else be so kind as to confirm the button does not appear correctly when using the small interface? Many thanks.

Hm.. I tried a practice match and tested small interface out with Verdic Messenger and som Psions. It worked for me.

I had a look in my options and realized I'm also using Small one - but I didn't notice any of the problems you're talking about so far, sorry..

Well, my mother always told me I was special. Thanks for checking guys.

Jed/Altren,
I’ve wiped all my temporary internet files, cookies, and associated files. I’ve deleted and reinstalled the downloadable client. The problem is still happening on the small interface but not the others.
Even more interesting, when I log in as a guest, I can use a card’s special ability on the small interface with no problem. Really makes me think the problem is not on my end.
I can get used to the dynamic interface, but I really like the small interface better. Can you think of anything else I can try? If need be, can we arrange for one of you to watch a match of mine so you can see what I’m talking about?
Thanks.

In options there is a "Disable specials pop-up" checkbox. Is that checked? uncheck it if it is.

sooo.... ummmm.... Can't say I ever noticed that little box. Must have accidentally checked it.
Thanks for pointing out the obvious to someone who needed it.