An internal error occurred during Launching TestNG File

The TestNG File issue is basically being caused by the presence of TestNG M2E in your installed software list. What you need to do is just remove TestNG M2E, your problem will get resolve. 

Steps

1.   Click Help menu.

2.   Click on Install new Software.

3.    Now click on “What is already installed?” as shown in the picture below.

4.   It will open a new window showing , already installed software on your eclipse.

5.    Select the TestsNG M2E from the list  as shown in the picture above and click on Uninstall button.

6.   It will ask for restart , click on Yes.

Wait for Eclipse IDE to restart . When eclipse get will restart go to your program and click on Run your script through TestNG.

Note: Still your getting same error, just Uninstall TestNG from eclipse and Try to install TestNG Only (exclude TestNG M2E) then try to run your script.