Added a trap when trying to populate a dseries object with...

... a datafile which does not exist.

src/@dseries/subsref.m

@@ -200,7 +200,11 @@ switch S(1).type
     if ischar(S(1).subs{1}) && ~isdate(S(1).subs{1})
         % If ts is an empty dseries object, populate this object by reading data in a file.
         if isempty(A)
-            B = dseries(S(1).subs{1});
+            if exist(S(1).subs{1}, 'file')
+                B = dseries(S(1).subs{1});
+            else
+                error('dseries::subsref: Cannot find file %s', S(1).subs{1})
+            end
         else
             error('dseries::subsref: dseries object is not empty!')
         end