Are there known issues calling powerbuilder 12 automation via Web app running on IIS?

We have few clients that have been running our web application using asp.net on IIS. We used to instantiate the Powerbuilder Automation within the web app to be able to call functions in one of the powerbuilder objects. The librarylist and objectname were provided and it worked fine using Powerbuilder 11 on IIS 6. Now we have upgraded and have a client that just received the Powerbuilder 12.1 version on IIS 7.5 and the Powerbuilder Automation initializes sometimes and other times it just crashes. There were moments in the EventViewer we got a pbvm120.dll error. We have not encoutered this issue previously nor can we reproduce this in our local environment. See sample code below in VB.NET. The bold area of the code fails sometimes. Not sure if it is a concurrency issue, IIS environment issue or whether this is something that is not supported any longer.

[VB.NET code]

       Dim pb_1 As Object

      Dim pb_2 As Object

      Dim strLib As New System.Text.StringBuilder

Try
        m_cLogger.LogDebugger(DEBUGSTART, "LoadPBObject", "", m_Page)

                pb_1 = CreateObject("Powerbuilder.Application.12")  

        With pb_1
          .LibraryList = libraryList

          .MachineCode = False
          pb_2 = .CreateObject(className) 'create library pointer
          Return pb_2 'create object pointer
        End With
      Finally
        pb_1 = Nothing
        m_cLogger.LogDebugger(DEBUGEND, "LoadPBObject", "", m_Page)
      End Try

[VB.NET code]

Any ideas whether this is a known issue and how to resolve it?