If you run SMF 2.0 and are running the Downloads Pro plugin (around v4.1.8) from SMF Hacks, the plugin will start throwing errors if you upgrade to php 7 if you have the download rate limiter installed (ie the number of minutes a user needs to wait before they can download).

On the Mastering VAST forum, we have this enabled for the free membership group, as a way of controlling bandwidth, associated with the downloads.

The errors we were seeing were:

Call to undefined function mysql_num_rows()

The reason for this error is the deprecation of mysql_ functions in php 7.

Fortunately the fix is really easy.

Change line 9686 of Downloads2.php from:

$totalRow['total'] = mysql_num_rows($dbresult);

to

$totalRow['total'] = mysqli_num_rows($dbresult);

That's it.  Save the file and refresh the  cache, and your users

SMF Hacks has confirmed that they have fixed this in later versions of their plugin.