Unable to step. Operation is not supported

Hi there,

I am getting the following error when stepping through code in Visual Studio 2015, I have re-installed visual studio, deleted temp/library/usr/suo files and I still seem to be getting the problem. Anyone else had this? I tried stepping through with mono, and it just doesn't want to work at all.

It seems to stop on this line :

 string selected = PlayerPrefs.GetString(playerPrefs);

It used to work fine so I am a bit confused.

Edit :I reverted to a previous version which stepping thru worked at, and it seems to still have the error, however I tried another project and it seems to step thru that project fine. I am at a bit of a loss right now. Rather frustrating.