android: R cannot be resolved to a variable

I'm developing an android application for a month. and today when I cleaned my project (project>clean...), I got "R cannot be resolved to a variable" error and i can't run my app.

I Googled for solution and did ever开发者_StackOverflow社区y solution for this problem but not success.

Note: I removed all imports R and cleaned my project again but the problem exists.

Can anyone help me?

Sorry for bad English!

Edit: problem solved. there was some errors in one of xml files.

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this appears when you have errors in layout files or other xml files. Also take care that images have names that don t contain upper caracters

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I solved my problem

LinearLayout android:id="@id/TelNoLayout" 

replace to

LinearLayout android:id="@+id/TelNoLayout"

and build