AE error: internal verification failure {child not found in parent}

I just had a similar issue. Turns out the effects I had on that layer were causing the same error. I deleted the effects and it worked fine.

Impossible to know. You have not offered any details on how the original project was even set up, so this is realyl not going anywhere and everything is just speculation.

Mylenium

Update: I've created a new text layer and it worked. The error could've been from some of the effects that were on the layer, although they were deactivated. It would be interesting to know. 

Thanks