>You're right about that, but that's the latest solution we will try to implement in our application. I already got a solution using the createmutex, openmutex and releasemutex in our application, but these functions deliver me another problem.
>
>When I start the first application, I create a mutex with the name "App1", de next time a mutex with the name "App1" cannot be created, so I create a mutex with the name "App2". De third time I start my application, when I create a mutex with the name "App1" or "App2", on both creations I get an error. When I quit my first app ( the one which created mutex "App1" ), I cannot run my app again. When I quit my second application, and first application is still running, I can run the application for a second time.
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>The problem now is how to determine my first app (with mutex app1) is closed. This time, my mutex "app1" isn't released in my first app.

I suggest you look at my CLSEvent download in the files section; it uses named Windows events to enforce single-instance anythings. Events do disappear when all event handles are released by all processes on a system; the sample single instance code I show does not create multiple handles to the same event if the single instance functionality is used.