Encountered an unexpected exception - 14w17a server crash

Whenever I try to start up my 14w17a server, it gives me an error with the line "Encountered an unexpected exception" Then saves a crash report.

*What I expected to happen was...:
The server would start up normally as usual.

*What actually happened was...:
Instead the server crashed.

Steps to Reproduce:
1. Start the server.
2. Notice the error and crash in the console.