报错代码：

SqlParameter voteFrom = new SqlParameter("@voteFrom", workFlow.VoteFrom);
SqlParameter voteTo = new SqlParameter("@voteTo", workFlow.VoteTo);
SqlParameter result = new SqlParameter("@result", SqlDbType.NVarChar,50);
result.Direction = ParameterDirection.Output;

context.Database.SqlQuery<string>("exec [workflow_CheckAccount] @voteFrom,@voteTo,@result out", voteFrom, voteTo,result).FirstOrDefault();//报错行。
checkResult =(string)result.Value;

换成下面方法通过：

List<SqlParameter> paramArray = new List<SqlParameter>();
paramArray.Add(new SqlParameter("@voteFrom", workFlow.VoteFrom));
paramArray.Add(new SqlParameter("@voteTo", workFlow.VoteTo));

SqlParameter param = new SqlParameter("@result", SqlDbType.NVarChar, 50);
param.Direction = ParameterDirection.Output;
paramArray.Add(param);
try
{
    context.Database.ExecuteSqlCommand("EXEC [workflow_CheckAccount] @voteFrom,@voteTo,@result out", paramArray.ToArray());
}
catch (Exception ex)
{
    throw;
}
checkResult = (string)paramArray[2].Value;