Calling VB6 exe using VB .Net applications login credentials

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VB6

VB

.NET

.NET4

process

I have a VB .net Windows application and on certain click i want to open a VB6 application , I used "Shell" to open the VB6 exe successfully but its obvious opening the login page. As the user entered the login credentials in the VB.net application already I don't want user to key in the credentials agian.

My effort:

Dim startInfo As New ProcessStartInfo()
startInfo.UseShellExecute = False
startInfo.FileName = "POS.exe"
startInfo.UserName = "ADMIN"
Dim testString As New SecureString()
For Each ch As Char In "pass1234"
    testString.AppendChar(ch)
Next
startInfo.Password = testString                       
Dim exe As Process = Process.Start(startInfo)

I did the above part in VB.net application and passed the UserName and password explicitly. But it is prompting the error as "Unkown UserName or bad password"

Do i need to amend Vb6 application too on the project load? or To create some GLOBAL parameter in VB6 to catch the UserName or Password sent from VB.net program and to check if these parameter exists then to perform the VB6 application's login screen's login button click.