Rehosting workflow designer

I'm creating an application that rehost the workflow designer and that can load an xoml only workflow.

When I deserialize my xoml-only workflow. There is an error stating : {"Could not deserialize object. The type 'MyCustomActivity' could not be resolved."}

my xoml looks like this:

<SequentialWorkflowActivity x:Name="Workflow2" xmlns:ns0="clr-
namespace:MyCustomActivities;Assembly=MyCustomActivities, Version=1.0.0.0, 
Culture=neutral, PublicKeyToken=null" xmlns:x="http://schemas.microsoft.com/winfx
/2006/xaml" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/workflow">
<ns0:MyCustomActivity x:Name="myCustomActivity1" /></SequentialWorkflowActivity>

I'm kinda stuck on this, my workflow is pretty basic. I just want to load it to see if I could see it.

MyCustomActivities is a library containing all my custom activities.