vs2012报这个错啥意思

[解决办法]
var reportQuery = from a in examReportTable.AsEnumerable()
join b in rvuTable.AsEnumerable()
on new{exam=a.Field<int>("exam"), examtype=a.Field<string>("examtype")} equals new{exam=b.Field<int>("rvuName"),examtype=b.Field<string>("rvuType")}
group b by new{ a.reportDoc,a.examtype } into c
select new YourClassName
{
};