Hi guys, i've got the same issue - trying to import templates used in "lesser" systems and created by external designers from days long gone, and while I've cleaned a lot of the HTML code up - this error has got me completely stumped!
I can do really basic HTML but the answers you guys have posted have also got me stumped.
I wouldn't even know what line of code to paste here to show someone.
What should I be looking for in the HTML, and what should it look like when it's correct?
Below is a sample HTML of a region I would to be editable;
<tbody>
<tr>
<td style="padding-top: 9px;padding-left: 18px;padding-bottom: 9px;padding-right: 18px;mso-table-lspace: 0pt;mso-table-rspace: 0pt;-ms-text-size-adjust: 100%;-webkit-text-size-adjust: 100%;">
<table border="0" cellpadding="18" cellspacing="0" class="mcnTextContentContainer" width="100%" style="border: 1px solid #999999;background-color: #EBEBEB;border-collapse: collapse;mso-table-lspace: 0pt;mso-table-rspace: 0pt;-ms-text-size-adjust: 100%;-webkit-text-size-adjust: 100%;">
<tbody>
<tr>
<td valign="top" class="mcnTextContent" style="mso-table-lspace: 0pt;mso-table-rspace: 0pt;-ms-text-size-adjust: 100%;-webkit-text-size-adjust: 100%;color: #606060;font-family: Helvetica;font-size: 15px;line-height: 150%;text-align: left;">
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</td>
</tr>
</tbody>