Weird error in Eclipse with Android -

It has not started until today, but I'm wondering what is happening because of it. Whenever I compile, as if only one of the 10 times is shown 2 errors, which indicates

  this.onBackpressed ();   
 and  
  Android: Theme = "@Android: Style / Theme. Holo"   
 both of which API level of 5 'is required' or API level of 16 'is required.  
 The point is, projects & gt; & Gt; Clean it every time, because it works fine, every time I do this, but it just keeps happening. What could be the reason for this?   
 
 
 These are errors, which warn you that you are using the API level attributes More than  minSdkVersion  (your  AndroidManifest.xml ). For example, the API was introduced in level 5. Trying to call it will cause an accident from an API level 4 or less device to the application.  
 Of course, if you run it on device API level 5 or higher, then your application will work fine, so why it always seems to work.