It happens while we import the project. To solve the issue you can try the following way
1. Project->Build Automatically then try
2. Project->Clean the selected project then try
If the above procedure doesn't work try the following.
3. Project->Properties->Compiler Settings
Check HTML Wrapper and If Not checked checked and try.
If the HTml Wrapper is checked the un-check then save then try to run it again.It will not work then again check the HTML Wrapper and try. I got it solved the issue.