I have had the same issue on multiple sites, a few of which were not running Shape 5 themes. Unfortunately, I was on a deadline with those sites and didn't have enough time to figure out the problem before I had to just move on to another solution. I believe I ended up using embedded Google forms.
The Shaper/Injector wipes the WP database and replaces it with a copy of the database from the demo; it's very possible that because you already had the contact form plugin installed before running before the injector, something could have changed in the database that conflicts with something already done by the plugin.
You may be able to solve the problem by using a database cleanup/repair plugin like WP-Cleanup; I just can't make any guarantees that it will work.
Let me know your results, and maybe we can work together on coming to a solution.
Thanks for the response. I tried to use WP-Cleanup and WP Cleanup plugins but no luck. Don't know what to do...