The value 'some value' is invalid when submitting form with checkboxes in MVC 5

I have a form in an MVC 5 application that has several checkboxes to allow different categories to be selected. However when submitting, I get the message The value 'some value' is invalid. That appears where the error message is for the checkboxes. I have looked and not found a solution.

I have an editor template:

@Modeltype ienumerable(Of be_Categories)
@For Each x In Model
      @<label>@x.CategoryName</label>
      @<input type="checkbox" name="PostCategory" value="@x.CategoryID"/>    
Next

And in the form I call:

   @Html.LabelFor(Function(model) model.PostCategory, htmlAttributes:=
       New With {.class = "control-label col-md-2"})
    <div class="col-md-10">
      @Html.EditorFor(Function(model) model.PostCategory,
         New With {.htmlAttributes = New With {.class = "form-control"}})
      @Html.ValidationMessageFor(Function(model) model.PostCategory, "",
         New With {.class = "text-danger"})
    </div>

And in controller:

  Public Function CreateNewPost(ByVal post As be_PostsViewModel) As ActionResult
        If ModelState.IsValid Then

            Dim p As New be_PostsViewModel              
            p.PostTitle = post.PostTitle
            p.PostDateCreated = post.PostDateCreated
            p.IsPublished = post.IsPublished
            p.PostGuid = Guid.NewGuid
            p.PostSummary = post.PostSummary
            p.PostText = post.PostText
            p.PostCategory = post.PostCategory
           _POSTREPO.Insert(p)

            Return RedirectToAction("Index")
        End If
            Return View(post)
    End Function

Can someone tell me where I am going wrong?