SSIS:Dts脚本任务在用户代码中遇到异常:异常被调用的目标抛出

包含脚本任务的包显示如下错误

Dts Script task has encountered an exception in user code:
Exception has been thrown by the target of an invocation

脚本任务代码为

public void Main()
        {
            string Str_Filepath = Dts.Variables["User::FilePath"].Value.ToString();
            bool bl_exist=false;

            if (System.IO.File.Exists(Str_Filepath))
            {
                bl_exist = true;

             }
             else
            { bl_exist = false; }
            Dts.Variables["User::V_Exist"].Value = bl_exist;

            Dts.TaskResult = (int)ScriptResults.Success;
        }