I wanted to post this to save someone some time.
I recently ran into an issue where I was trying to display a Paypal button on an article within Joomla. The button showed on the page, but when you clicked the button, it would send you to a Paypal page with an odd error. I was posting the Paypal button using the HTML form code they provide.
What I found out was, the email cloaking plugin was taking the email address in the form code and replacing it with Javascript. Once I disabled the email cloaking plugin, everything worked without any issues. You can disable/enable the email cloaking plugin by going to Extensions->Plugin Manager and clicking on the red circle/green checkmark in the Enabled column.
Thank you, I encountered the same issue and that fixed it.