I have the same bug, I'll try to post some more information, hope it helps:
Just like OP says, when I try to create a new world it says ''Error starting single player mode''
OS: Windows 7 Home Premium 64 Bit
CPU: i5 2500k
RAM: 8GB DDR3
GPU:R9 270X 4GB
Clientlog attached below.
clientlog_Tue_May_10_19-34-18_2016.txt