InvalidOperationException while accessing a navigation property

   Hi,
Following to this issue http://www.ideablade.com/forum/forum_posts.asp?TID=4674&title=systemreflectiontargetinvocationexception-in-silverlight-model
I noticed (CLR exceptions ON) many exception, close to 25, during a very long procedure on the server.

Since I find this procedure is taking too much time, I wonder if those exceptions could slow down a lot the procedure like it was for the previous issue.

I get this one a lot, most often when I access a Navigation Property (RelatedEntityList)

L'exception System.InvalidOperationException s'est produite
  _HResult=-2146233079
  _message=Cannot invert - root level projection
  HResult=-2146233079
  IsTransient=false
  Message=Cannot invert - root level projection
  Source=IdeaBlade.EntityModel
  StackTrace:
       à IdeaBlade.EntityModel.Edm.Shared.NavigationPropertyExpressionVisitor.VisitCall(MethodCallExpression mce, Expression objectExpr, IEnumerable`1 argExpressions)
  InnerException: 

I don't understand why I get these exceptions. I tried toi deactivate or set to manual the QueryInversion on my entitymanager, but I still get them.
Does it means my model is wrong or that the previous query I used to load parts of these data are incomplete ?

I also get this kind of exception.

L'exception System.InvalidOperationException s'est produite
Message: Une exception de première chance de type 'System.InvalidOperationException' s'est produite dans IdeaBlade.EntityModel.dll
Informations supplémentaires : Unable to construct inverted path for:
Type: MyApp.Module.Domain.Entities.MouvementDetail  Property: Mouvement
Type: MyApp.Module.Domain.Entities.MouvementDetail  Property: PeriodesGenerations