Error in crystal report 2011 that needs db_crldp.dll file

When using crystal report 2011 in vb.net 2010 in net framework 4.0
a mysterious error occurs that needs some file like db_crldp.dll ????
sol:
paste this in the app.config:

  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0"/>
  </startup>