DD won't download

[Thomas]

So at least in one case it works ? That's very strange....

> i don`t thing this is the problem because it would notify me if it blocks something

I have no experience with Symantec Endpoint in particular, but not all security programs notify about everything they do, and some only display notice for a very short time.
You could try to grant Device Doctor more rights in Symantec Endpoint, if at all applicable in that software, or disable Symantec Endpoint for a very short time to test whether that would have any effect (of course only if your security situation allows).
Other than that I'm running out of ideas I'm sorry, except to try different build from http://www.devicedoctor.com/device-doctor-builds.php, ie. the portable one in case you are currently using the standard build.