Startindex cannot be less than zero when trying to create a sample xml file from a xsd file

Using Visual studio pro 2015

I have a xsd file and need to generate a xml sample file from it.
Ive opened the file with the XML editor. When i Try to "Generate Sample XML", I'm met with the following:

Have anyone experienced this?

Any hints or tips on how to find the fault are welcome!

brgs

Bjørn