abhgupta ,
Sorry that you are seeing this issue.
1) Can you please share your Operating System and version details ?
2) Can you start the IDE with -clean and check if the issue persists ? If yes then can you try a new workspace ?. Here is the FAQ for -clean : https://www.genuitec.com/forums/topic/troubleshoot-using-the-clean-command-line-argument/
3) Did you make any changes to the IDE since you last started it successfully ? Did you install Flex plugin ?
4) Can you also clarify if you have upgraded to version 9.1 ?