Question

The Flash Builder restart after showing this alert.

Unhandled event loop exception 
unable to create new native thread

Note That i am using Flash Builder 4.6

Thanks

Answer 1

Do you have a big project with lot of files and libraries?

In my experience, this is caused by low Java memory.

Option A: Solution is to increase memory for Flash Builder.

Adobe says: Improving Compiler Performance for Large Projects

Edit FlashBuilder.ini lines with Xms and Xmx

-vmargs
-Xms512m
-Xmx1024m
-XX:MaxPermSize=256m
-XX:PermSize=64m

My computer with 8 GB RAM allows max increase for 1g, not more. We have project so big that we were forced to migrate to IntelliJ IDEA with external compiler

Link: Maximum for Java VM is discussed here

Option B: Create new Flash Builder/eclipse workspace and recreate your project. (Or remove .metadata folder from your workspace).

Maybe there are some local changes that corrupted something inside the Flash Builder.

Can you reproduce the same error on another PC?

Option C: Leave Flash Builder and migrate to other software. I suggest IntelliJ IDEA which uses external compiler and that way the compilation process can use more memory (Flash Builder shares its memory with the compiler).