Thank you for contacting us, icewazza.  I just did some testing and found the same problem.  At first, it successfully deleted a half dozen or so bookmarks  (or "posts", as they call them), so I thought they had tightened up their throttling limits.  But then after waiting an hour it still got stuck on deleting one particular bookmark/post, so I'm not sure what the problem is.

As the error message from Diigo suggests, I sent an email to service@diigo.com explaining the problem in technical detail.  To help get their attention, it would be good for you to send such an email too.  The more emails they get, the more likely we are to get a resopnse, particularly from people with paid Diigo accounts.

You can tell them the following.  Copy and paste if you want to:

The trouble started suddenly with the app BookMacster.  BookMacster has not changed its Diigo-related code for many months.  BookMacster is using the "v2" (version 2) API.  For further information, contact BookMacster developer Jerry Krinock, jerry@sheepsystems.com, and/or read the email from jerry@ieee.org which has more technical detail.