When you say a collection, what type is this?  Ienum, List?  When you say items in the collection what types are these?  I dont understand when the error is occuring :).  Charlie.

Yeah, sorry I should have really provided more info :)

For example, I have a page which lists a node collection of a particular along with their properties. One of those properties is of date type, which may or may not contain a value, but would like to order by it as best as I can

I had to revert back to linq to get around this..

DynamicNode[] nodelist = homePageNode.DescendantsOrSelf().Items
                                .Where(x => x.GetPropertyValue("hideInNavigation") != "1"
                                    && x.HasAccess
                                    && x.Level <= level
                                    && (DateTime.Parse(x.HasValue("ExpireDate", x.GetPropertyValue("fidusCMSExpireDate"), DateTime.Now.AddHours(1).ToString()).ToString()) > DateTime.Now)
                                    && (DateTime.Parse(x.HasValue("ReleaseDate", x.GetPropertyValue("fidusCMSReleaseDate"), DateTime.Now.AddHours(-1).ToString()).ToString()) < DateTime.Now)).ToArray();

Thanks for the reply Mike.

How could this approach be used with the OrderBy() method though instead of inside a Where()?

Simon 

maybe something like 

OrderBy(x => x.HasValue("ExpireDate", x.ExpireDate,DateTime.Now))

eg if no date then use time now.. or your choice of how to deal with no set date.

Hmm thought you might say that ... trouble is I'm working within a Razor macro and am I right in thinking you cannot use the predicate within the OrderBy() and must provide a string representation? Correct me if I'm wrong; I'm still pretty new to the Umbraco world! 

i think thats correct but dont work with macros, will read up on them :)

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