What causes this issue?
Safari prevents Acrobat from running in your browser. This results in "Blocked Plug-in" appearing on your page. This is because you're using Preno in Safari and Adobe Acrobat Reader is configured to your default program for opening .PDF files. It's not caused by Preno. It affects both the generation of Receipts and Registration Cards.
How do I get rid of this error?
There are a few solutions, and the most reliable way to fix this is to use the latest version of Google Chrome.
1. Use “Open link in new tab”:
Right click on “Registration” or “Receipt”
Choose “Open Link in New Tab”.
2. Set the native PDF viewer, “Preview” to open all PDFs:
Find any PDF file in Finder
Right click on it
Choose “Get Info”
Under “Open with:” choose “Preview” and click “Change All…”
Right click on any .PDF in Finder, and then select Get Info.
At the bottom, change the 'Open with:' to Preview, and then click Change All.