Created Unassigned: Cannot Compile Prism 4.2 as well [10568]

When I try to compile Prism 4.2 I've got following error:

Error 1 The remote server returned an error: (407) Proxy Authentication Required. Prism.TestSupport

Via TCPView i can see a connection trial on local port 6999 (is that a TFS port?):

[System Process] 0 TCP 127.0.0.1 6999 127.0.0.1 57877 TIME_WAIT

Any idea ?

Thanx
Peter