新增CrystalReport報表至VS2010 WindowsApplication執行出現The type or namespace name ‘CrystalDecisions’ could not be found (are you missing a using directive or an assembly reference?)

狀況：新增CrystalReport報表至VS2010 WindowsApplication執行出現The type or namespace name ‘CrystalDecisions’ could not be found (are you missing a using directive or an assembly reference?)，
但是CrystalReport1.cs已有宣告
using CrystalDecisions.Shared;
using CrystalDecisions.ReportSource;
using CrystalDecisions.CrystalReports.Engine;
而project的reference也有此3項dll。
解法：將project的properties ==> Application ==> Target framework ==> 由.Net Framework4 Client Profile 改為 .Net Framework4，
就可以complier及執行成功了~~
原因：尚不知解法之原因…