Howto use configurable Merge Modules in Wix?

Question

AFAIK it's done like this:

Product:

<Merge Id ="HelpInstaller" SourceFile="HelpInstaller.msm" Language="1033" DiskId="1">
                <ConfigurationData Name="SurpressInstallation_Config" Value="&amp;HelpFeature"/>
 </Merge>

Merge Module:

<Property Id="SupressInstallation" Value='0'  />

<Substitution Table='CustomAction' Row='SetSupressInstallationProperty' Column='Target' Value='[=SupressInstallation_Config]'/>
<CustomAction Id='SetSupressInstallationProperty' Property='SupressInstallation'      Value='[SupressInstallation]'/>  
<InstallExecuteSequence>
  <Custom Action='SetSupressInstallationProperty' Before='RegisterHelp' />
  <Custom Action='RegisterHelp' After='CostFinalize'>(NOT Installed) AND (NOT UPGRADINGPRODUCTCODE) AND SupressInstallation = 3) </Custom>
</InstallExecuteSequence>

But when i did it like above i get an error: Encountered an unexpected merge error of type 'msmErrorDataRequestFailed' for which therer is currently no error messagte to display.

Can anyone tell me howto solve that problem? What i basically want to do is to execute a custom action in the merge module only when a certain feature is selected..Is this the right way to do it? Thanks Daniel