Strange error on stringed Linq calls - iterator

Question

I inherited this code that takes an IEnumerable and performs a series of Selects on it and then attempts to call Sum on the remaining records after the Selects are performed. The code reads as:
var totalrecs = records.Select(row => new RowInfo(RowID = row.RowID, SomeData = row.SomeData})
.Select(ri => new {RowInfo = ri, XMLData = GetXMLFileForRecord(ri)})
.Select(data => ParseAndUpdateRecords(data.RowInfo, data.XmlData))
.Sum();
where 'records' is an IEnumerable.
The error is for attempting to convert a decimal to a long and from the StackTrace seems to be occurring when calling Sum on the Iterator that results from the three Select calls.
The stack trace is:
Exception:Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: Cannot implicitly convert type 'decimal' to 'long'. An explicit conversion exists (are you missing a cast?)
at CallSite.Target(Closure , CallSite , Object )
at RecordCapture.Controller.<CaptureAndUpdateRecords>b__10(Object row)
at System.Linq.Enumerable.<>c__DisplayClass12`3.<CombineSelectors>b__11(TSource x)
at System.Linq.Enumerable.<>c__DisplayClass12`3.<CombineSelectors>b__11(TSource x)
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Linq.Enumerable.Sum(IEnumerable`1 source)
at RecordCapture.Controller.CaptureAndUpdateRecords()
at RecordCapture.Controller.<Start>b__1()
StackTrace: at CallSite.Target(Closure , CallSite , Object )
at RosterCapture.Controller.<CaptureAndUpdateRosters>b__10(Object row)
at System.Linq.Enumerable.<>c__DisplayClass12`3.<CombineSelectors>b__11(TSource x)
at System.Linq.Enumerable.<>c__DisplayClass12`3.<CombineSelectors>b__11(TSource x)
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Linq.Enumerable.Sum(IEnumerable`1 source)
at RecordCapture.Controller.CaptureAndUpdateRecords()
at RecordCapture.Controller.<Start>b__1()
The Selects return an Iterator and there does not seem to be any way to get an accurate count of what the result of the Selects is.
Interestingly, if records is empty, calling Sum simply returns a zero and does not throw an error.

Answer 1

Do you want to Sum integers or decimals? Use the Generic type appropriate, and cast the result if necessary. See http://msdn.microsoft.com/en-us/library/system.linq.enumerable.sum.aspx for the overload list.

Answer 2

I figured this out. The Stack Trace was misleading.
The issue was in building up the RowInfo object in my code... the RowID was a long and the variable that the property was setting it's value to was a decimal.
I believe the error occurred in the Sum call because of lazy loading where the setting of the attributes was not done until that call was made and the data was needed.