Some things to check: 1. How are you starting it outside of your application? If you are using a short-cut or a batch file, check to make sure you are using the same commad-line parameters. 2. I believe only 1 application can have the COM port open, so are you sure it's not already open when you launch it from your application? 3. Are you launching the application using the same credentials? If you are changing users in your application (using impersonation) or are launching your application as a different user, then maybe that person doesn't have rights. This includes rights to open the COM port and/or write to the "download" directory, if any. 4. Finally, as a test try launching it using a small test app that only starts the third-party app. This would help rule out ProcessStart as the culprit. Take care, Tom ----------------------------------------------- Check out my blog at http://tjoe.wordpress.com

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