strange error when i import example
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and thanks for your help

i download the example of android book "android 4 application develop", now i import the project but i see i have in console this error 
[2012-07-31 12:07:13 - PA4AD_Ch09_MyService] Unable to resolve target 'android-15'
and in the all class i have this: 
`import android.app.Activity; 
// for all import pachage`
I have this error:  The import android cannot be resolved
I see this error for all import package
if i create a new project all work well.
when i used android sdk tool 15 all work well, now i don't know to do, can you help me? 

best regads
Antonio