Entity framework mapping enum : The specified value is not an instance of type 'Edm.Int32' Parameter name: value

Enums in projections from Entity Framework projections (Select) is a know issue. If you do

_entities.Price.Where(p => p.StatusCode.Equals("A") &&
    p.Period.PeriodYear <= DateTime.Now.Year + 1 &&
    p.Route.RouteCode.Equals(routeName)).ToList() // ToList !
    .Select(p => new Trade ...

the projection is done by regular linq-to-objects, which is a routine job.

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EDIT

As a late afterthought I'd like to add that just a dumb ToList() can be detrimental when the table in question has many columns. It would mean that far more data is transferred to the client than necessary. In such cases it can be useful to do a double projection. First, within the scope of the query provider project to accepted types. Then, after switching to linq-to-objects (AsEnumerable) project to the final type:

_entities.Price.Where(p => p.StatusCode.Equals("A") &&
    p.Period.PeriodYear <= DateTime.Now.Year + 1 &&
    p.Route.RouteCode.Equals(routeName))
    .Select(p => new 
                {
                  Volume = (long) (p.Volume ?? 100), 
                  PriceTypeCode = p.PriceTypeCode,
                  Price = p.Price1,
                  TenorStartDate = p.Period.PeriodStartDate.Value,
                  TenorEndDate = p.Period.PeriodStartDate.Value,
                  TradeId = p.ID
                })
    .AsEnumerable()
    .Select(x => new Trade
                 {
                   Volume = x.Volume, 
                   TradeType = (x.PriceTypeCode.Equals("O") ? TradeType.Seller : TradeType.Bidder),
                   Price = x.Price1,
                   TenorStartDate = x.TenorStartDate,
                   TenorEndDate = x.TenorEndDate,
                   TradeId = x.ID
                 }).

Installing .Net 4.5 appears to fix the issue as well (your project can still be on 4.0).

I was having this issue on our staging server (dev and test servers worked fine) and discovered that it did not have .Net 4.5 installed. Once I installed 4.5, the issue cleared up without any code changes.