Thank you for your post.
I would start by restarting the computer and see if the issue still occurs. If it does, you may want to run Recovery on the "Contacts DB.fmp12" as it could've been damaged when FileMaker crashed.
You might also try using a New Starter Solution to confirm it's not a software issue (bad install, software conflict, etc.).
TSPigeon thanks for taking the time to reply. I feel pretty dumb. After a web search I went back to analyze the situation from a more analytical point of view and discovered the problem. I still had the Contact file open. Once I closed it I was able to add the file and create the runtime. Sorry to waste your time but hopefully someone will have the same issue. I am new to making runtimes so hopefully you'll give me a free pass this time.