I've had several e-mails about the Add-In not appearing in Excel 2013 lately. Curiously not so much for Excel 2010, for which this should also be a problem with similar "Trust Center" settings. In any case, the problem was due to using a personal code-signing certificate for the Add-In rather than one of the... holding my tongue... somewhat more expensive code-signing certificates from MS-approved certificate authorities. Unfortunately getting the problem fixed will require some hoop-jumping on your part if you're having this problem.
- Start Excel. Go to File>Options>Add-ins, click Go next to "Manage Add-ins", uncheck "DPlot interface", click OK.
- Go to File>Options>Trust Center, click the "Trust Center Settings" button. In the left pane select "Message Bar". Ensure that "Show the Message Bar in all applications when active content, such as ActiveX controls and macros, has been blocked" is selected. Click OK twice and exit Excel.
- Download and save the updated Add-In to %appdata%\Microsoft\Addins, overwriting the existing version.
- Start Excel. You'll almost certainly see a security warning. If so, click on "Some active content has been disabled. Click for more details."
- Click "Enable Content", then "Advanced Options".
- You may see more than one "untrusted" offender. Look for "Signed by: HydeSoft Computing LLC". This may not be the first entry and you'll need to scroll through the list. Select "Trust all documents from this publisher" then click OK.
- Exit and restart Excel.
You should now see an Add-ins tab and when clicked see the DPlot Add-in just below the File tab. If not please let me know at firstname.lastname@example.org.