I'm assuming this is the official 5e OGL sheet. Are you popping the sheet out into it's own browser window? Drag and drop doesn't work with sheets that are in separate windows - they need to be open on the tabletop. If it is happening with sheets open on the tabletop, then I'd suggest trying the troubleshooting steps found here: <a href="https://app.roll20.net/forum/post/3/read-first-submitting-bug-reports-and-faq#post-3" rel="nofollow">https://app.roll20.net/forum/post/3/read-first-submitting-bug-reports-and-faq#post-3</a>