When you use RUNAS, you are actually logging on as a different user. It's most likely that rms\rmsuser doesn't have the R: mapped after login. If this is an occasional manual operation, try to RUNAS cmd.exe, then use net use to map the R: drive then run your app from the command line. If you need to do this all the time, create a batch file or VBScript to map the drive the launch the app, and RUNAS the batch or VBScript.