The thing is another application has already open the port before you run your program. Find out which application and close it before you run your vb program. Most probable cause is that the serial port is being used by a modem or mouse, under dos and windows, it is reserved before you are able to run your application. Disable the drivers if you are persistent to do that, or you might try to use another port.
In addition, you may remove temporary any add-on board on your machine like faxmodem or devices using the serial ports to automatically disable the device drivers.
:wink: :wink: :wink: