Failure to download purchased game after clicking Play.

*What I expected to happen was...:*That it would download as it said and Minecraft would just play then.

*What actually happened was...:*It says its downloading but after its finished it just stays on the same screen and then it quits out of Minecraft launcher 1.6.48 then it comes back on again and says that there is a crash report

Steps to Reproduce:
1. I open the mincraft launcher
2. I click play and it starts to download
3. once the whole bar goes blue so that it means its done it just stays on the screen until it quits and comes back on again and says there was a crash report please can u fix this asap please