While creating a windows application in visual Studio 2005 the application set up supports user launch multiple instances of the application on a PC simultaneously.

To avoid user launch multiple instances of the application, select the Make single instance application check box to prevent users from running multiple instances of your application.

The default setting for this check box is cleared, allowing multiple instances of the application to be run.

You can do this by following the steps below:

1) Right-Click on MyProject inside SolutionExplorer –> Open

2) Select Application tab

3) Set the Make single instance application checkbox Checked/Unchecked as per the requirement.