problem with listbox getting error

Hi Frinds,

We are using nwds7.0.0.9 and EP6.0 with sp16. we are trying to dvelop an application, in our view contains listbox(we are trying to featch vales from node and display in this listbox), but we are getting fallowing error

"java.lang.NoClassDefFoundError:comm.sap.tc.webdynpro.clientserver.uielib.standard.api.IWDItemListBox"

Please tell me why i am getting this error

Thanks

Gana