What error do you see?
Please ensure that you have given path for Editor exe while setting preferences. Check : http://help.adobe.com/en_US/lightroom/using/WS30BB1A73-0A01-4072-978C-56C8DE443A03.html
You generally open an image for external editing from the Lightroom library module. Select a thumbnail and press Ctrl+E
Also check that the PSE11 Editor application is recognized. From the library go to Edit >> Preferences
Then choose the External editing tab.
If the app is not shown in the top section, click the choose button in the Additional External Editor section. Then navigate to PhotoshopElementsEditor.exe