I solved the “widget disposed error” like this.
I am using Windows XP and my language is Turkish.When i tried to open myeclipse,i got this error.When i was trying to fix this error,i changed the language of Windows to English(USA) from Control Panel->Language Preferences.So when i reponed myeclipse,i didn’t get the error.I can use visual editors now.So if you set your Windows language diffirent from English,changing it to English may help you.