Another thought is that many custom themes require one of the default BlackBerry themes to be installed for the custom theme to work. If your Berry only has one theme installed, maybe it needs another of the default Berry themes to be installed for your custom theme to work.
"BlackBerry's texting in the dead of night. Have you no shame? No time's not right. You're a sorry sight. Hand over the device and everything will be alright. Put the crack away and everything will be alright. There's more to life than waiting for a message to arrive."