You know, it sounds like you've used the latest version from the releases page where the Open(XmlDocument) method wasn't implemented yet unfortunately.
If you download the latest source code and compile it the Open(XmlDocument) method will be implemented.
If you don't want to do that there is another option:
var doc = SvgDocument.Open(Resources.ResourceManager.GetStream("My.Full.Namespace.ErrorImage.svg"))*
It's not as pretty as the current option but it should work.
Let me know how you get on.
* - I think you'll need the full namespace plus the name of the file (& extension) in there but it might work with just the file name & extension; I don't think I've used that particular API before.