That was in response to #836 and the following information you provided :

With Excel 2013, we have a work-around to get over a problem which Microsoft have introduced with 2013. They changed some of the internals, which means we can’t embed excel inside EA. instead, excel will run in an external window. Same function, but not quite so nice to use. We are trying to get Microsoft to fix this problem, or at least document a work around, but they seem surprised by the issue!

-> I’m getting this embedded window issue with Excel2013. I agree this should be a new thread (not related with the NullRefException)