Command to Create OmniFocus Task from E-mail Message Stopped Working

Running MailMate Version 1.9.3 (5164) and OmniFocus 2.0.4 (v87.19 r222363) on OS X Mavericks 10.9.5, when I select an e-mail and use Command | OmniFocus | Add with Summary or Command | OmniFocus | Add to turn the e-mail into an OF task, OmniFocus responds with the following dialog box:

Cannot insert an instance of “__NSCFString” into the characters array.

OF creates a task in the Quick Entry window whose task title is the e-mail subject line.

The expected behavior, which worked well up until a few days ago, was that OF would create a task whose title is the e-mail subject line and whose note is the note of the e-mail message along with a "URL" to the message in MailMate.

According to the MailMate Preferences, the OmniFocus bundle was updated 6 days ago.