When you run the recorded macro, sizepic(), "Picture 4" already
exists, your only selecting it.

It looks like your code might work if you know for certain
XLRow.ToString() is 4 and from within C++ you're opening the Workbook
that has a "Picture 4" Shape.

If you are creating the Workbook dynamically then the problem is that
you don't have a shape object of name "Picture " + XLRow.ToString() .

Supposing you have added it then the problem is that you used a
barebones API to create the Shape and the Shape doesn't yet know it's
supposed to be a Picture.