Windows phone 8 build error

For Windows Phone 8 gives the following error when I try to get the output.I reinstall Unity 3D but the problem did not improve.

Error building Player: Exception: Failed to run assembly preprocessor with command line “Temp/StagingArea/Data/Managed\Assembly-CSharp-firstpass.dll” -injectCtor -assemblyPath “Temp/StagingArea” -pdb.[Temp/StagingArea/Data/Managed\Assembly-CSharp-firstpass.dll]

Try looking for abstract Unity functions like “abstract void Start”. Commenting out an abstract Update function solved this problem for me after I painstakingly deleted (and later restored) most of my project to find this error.