It should be due to Java heap size error.
If it is running for long time, try to close the DT studio. It will throw an error pop up with Heap size x256 error.
Change your heap size in Start -> Programs -> Data transformation -> Configuration -> (General -> Java -> Max heap size change from 512)
It worked for me. Let me know about your side after doing this.
I tried with changing heap size - it worked for me.
I put the Heap size as 1024 because my current setting is set to 512.
Thanks Pradeep for the solution.
Has the DT Studio hung problem resolved? If so, was it due to increasing java heap size?