For an example on how to send and receive data between different instances of the same script and which passes commandline parameters to the first instance via WM_COPYDATA take a look at post 2. Just a short snippet which came to my mind as the _Singleton() standard UDF failed on my work-notebook for me (CreateMutexW returns winapi-error 126 - "The specified module could not be found" , I just assume it interferes with one of the 72 processes running). #cs -----------------------------------