A snipping tool only attaches pics to the mail. Shouldn't have anything to do with the ost file being in use
OUtlook 2016 shouldn't have a separate button for send as attachment. If you have this button it could be an OUtlook addon that want to make use of your ost file and can't because outlook itself is using it.
You could try
- save the photo file to your local computer from the snipping tool and just drag the picture from the saved location in a folder to your e-mail body (or try Ctrl V into your mail after snipping)
- click the normal Send mail button that works.