I think I had the same issue moments ago. I had purchased the Deluxe download. and when I was ready to file Turbotax was asking me how I wanted to pay for it? I just forked over $80.00 (but should have bought through Costco! $49. for the same thing. but back to the issue, It went into a tail spin and wouldn't go any further. I simply exited fully out of the software and re-entered opening my current tax return and it finally went through.
Give that a try and if it does not work look for the support button within the software. Hope this helps!
~Michael