Vista only allow so many applications to run?

My installation of Windows Vista prevents me from having so many applications running. For example if I have the max amount of applications open and I try to open a application from the start menu I hear a windows ding noise and the application does not launch;the start menu stays up like I didn't do anything. If I close a window (like a window of internet explorer) then I try to launch the application it runs it fine.

It is terribly annoying since Vista will only allow me to have 13 or so windows/applications running. This problem has developed in the last 2 weeks or so and I have had Vista for 2 months. I checked for virus's with Avast. I am not sure if Microsoft released a upgrade for Vista that does this. My computer is very vanillia (meaning its adverage).I havnet installed any new applications that would cause this problem.

I think its a MS service but I am not sure which one.

Help would be appreciated .

Thanks

Vista only allow so many applications to run?norton internet security

Because Vista is so new, I'm sure it's something that Microsoft is working on. I personally haven't run in to the problem. Try googling it or finding a topic in a forum.