Cannot change Language when UseCurrentUICulture is on

This error occurs since you forgot to set the UseCurrentUICulture to false when instantiating the MetaDataContext object The error message looks something like this MetaDataPlusException was unhandled Cannot change Language when UseCurrentUICulture is on To solve this you simple need to set the UseCurrentUICulture to false when instantiating your MetaDataContext object, in example

MetaDataContext metaDataContext = new MetaDataContext(connectionString)
{
    UseCurrentUICulture = false,
    Language = MyProject.EPiServer.Constants.ProductCatalogConstants.DefaultLanguage
};