Well, that's very likely not what the server thinks considering other people can use the ability without worry.

Not that it's definitely client-side, but this problem certainly sounds as though it is. Does it happen every time, reliably? Does it happen when other players use it?

Does FFXIV have some sort of file integrity check feature? If so, it might be a good idea to use it. There are a myriad of client-side potential causes. Might also be worth reinstalling the game to see if that fixes it.