Cannot Byepass installation of prerequisites in custom Bootstrapper

Question

I have created a custom Bootstrapper package in vs 2010. But I cannot byepass the installation of prerequisites if it is already installed. If the prerequisites is already installed I need to skip the installation of prerequisites and continue installation of my application.

In Product.xml I have the following lines

  <Product xmlns="http://schemas.microsoft.com/developer/2004/01/bootstrapper"  ProductCode="Winpcap.Package">
<PackageFiles>
  <PackageFile Name="WinPcap 4.1.3.exe"/>
</PackageFiles>

<InstallChecks>
  <MsiProductCheck Product="WinPcapInst"  Property="IsMsiInstalled"/>
</InstallChecks>

<Commands>
  <Command PackageFile="WinPcap 4.1.3.exe" Arguments="">

    <InstallConditions>
      <BypassIf Property="IsMsiInstalled"  Compare="ValueGreaterThan" Value="0"/>
    </InstallConditions>

    <ExitCodes>
      <ExitCode Value="0" Result="Success"/>
      <ExitCode Value="1641" Result="SuccessReboot"/>
      <ExitCode Value="3010" Result="SuccessReboot"/>
      <DefaultExitCode Result="Fail" String="GeneralFailure"/>
    </ExitCodes>
  </Command>
</Commands>
</Product>

But I cannot skip the prerequisites installation. In installation log I have the following information

"Property: [IsMsiInstalled] = -2 {int} Result of running operator 'ValueGreaterThan' on property 'IsMsiInstalled' and value '0': false"

Cannot set the property 'IsMsiInstalled' if the prerequisite is already installed. Pls advice

Thanks in advance