Submissions with errorcode = 6 are retried forever

[thepurpleblob]

errorcode =6 is is the mystery condition that reports the error, "...there is a problem editing the module settings...". As an aside, this makes no sense and nobody has ever been able to explain what it means or how to rectify it.

However, if this does occur, the plugin retries these submissions forever. We have seen the number of 'attempts' reaching 10,000.

The bigger issue is that once there are a few hundred of these, they start to have a significant effect on queue performance. The plugin spends more time attempting to retry these than it does sending new submissions.