It sounds like you have to objects – the logo and the text – which are casting shadows, but you want to fade out the shadow from the text while keeping the shadow from the logo. If that is the case, then you have exceeded my limited knowledge. 😉
Perhaps you will need to render out two animations – one with the logo and its shadow, and one with the text and its shadow fading out – and then composite them in After Effects. Hopefully someone with more expertise can chime in.
Good luck.