In our solution we have several Custom Properties that work as expected. But when I add a new one and apply it to a page template, I get an error in edit mode:

Error: Can't load property type '(Namespace).CustomPropertiers.MyCustomProperty (NameSpace).Templates' 

This error appears as a JS alert when trying to expand the page tree in which the property is used. Everything works when I remove my custom property (or replace it with another).

I have made several attempts in creating the property with different approaches:

1. Visual studio wizard -> add new custom property
2. Copy/pasting the example in Denis Yakovlev's article http://world.episerver.com/en/Articles/Items/Creating-custom-properties-in-EPiServer-CMS-5/
3. Copying one of our existing custom properties  and replacing classnames

but the problem persists. I seem to have exhausted my alternatives, so any help in resolving this issue is greatly apprecciated 

Ps: this might be discussed earlier, but I was unable to find any similar posts.

PR