Excel OLE action error explained

While working in Excel, you may have seen this error pop up:

It will lock you out of your current workbook, and other workbooks that you may have open. This message may be prompted if you click on a link to a PDF on a worksheet, and then try to OCR it. The message will prevent you from continuing to edit in Excel until the OCR process has been completed. Clicking OK will not make it go away. Cancel text recognition in the PDF editor to get around this error message.