What do you have here?
I don't see substitution variables in the file you sent, but Toad is checking for them and that's what's causing this. So I'm not sure what's going on there, but...
If you set it to "none" and enter some obscure character for the prefix like `, does the problem go away? When I actually had a substitution variable in my file, I could make the error go away with this trick.
Edit: Does your SQL File contain a & character in some comments at the top? That could have caused this too. Toad is currently not ignoring those as it should, but I will fix that.