Linq to EF (EF4) deleting entry from many-to-many joining table

[xMetalDetectorx]

Entities:

Article
ArticleID

ImageMaster
ImageID
ImageType (1, 2, 3, or 4)

ImageArticle <-- this entity is produced by EF because of extra fields
ImageID
ArticleID
Title
Desc
Alt

I'm trying to delete all entries in ImageArticle where ArticleID=### and ImageType=4

I tried

foreach (ImageArticle ia in Article.ImageArticles.Where(i => i.ImageMaster.TypeID == 4))
{
   context.ImageArticles.Delete(ia);
}
context.SaveChanges();
 

But it gives me an error about foreign keys not being nullable.

I also tried Article.ImageArticles.Remove(ia), but then it wont let me iterate through the loop because the collection changed inside the loop.

The next thing I tried was gathering all the ImageIDs that I need to delete, then do this:

context.ExecuteStoreCommand("DELETE FROM ImageArticle WHERE ArticleID = " + Article.ArticleID + " AND ImageID in (" + IDs + ")");
context.SaveChanges();
 

But that also gave me the foreign key error.

How can I achieve deleting these rows in EF?

[xMetalDetectorx]

follow up:

ImageArticle
ImageID pk/fk (not nullable)
ArticleID pk/fk (not nullable)
Title
Desc
Alt