Hi all,  this has wasted 7 hours of my life and I am no closer to a solution.  But I do now have quite a lot of info.

Here is my issue which should be simple!

I have a custom object called 'Check'.  This represents a check to be added to a shift on an external system.  I am using outbound messages to send data to that external system.

The workflows and outbound messages work perfectly.  So I can tick a checkbox called 'active' for example, and it triggers a 'create check' outbound message.  When I uncheck the 'active' checkbox, it triggers the 'delete check' outbound message.

No problems, all working, data in both directions.

But wait, when I use dataloader.io to update records, the workflow rules all trigger, but now the outbound messages just sit in a queue and get re-attempted but never leave. Hence my data and the external system is not updated.

Even if I use a list view to say check the 'active' checkbox to true for 4 records, it will send one outbound message, and then put 3 in the queue.  Which once again doesn't move.

I've been monitoring the outbound message logs and the failure message is shown as:
org.xml.sax.SAXException: Bad envelope tag: div

I've spoken to my developer and he has no ideas.  It must be something to do with concurrent messages as one is fine but as soon as I do anymore it stops sending.

Please help developer peeps as I'm out of ideas and given i've got nearly 16,000 records to import, i'd rather not have to hire 10 staff to get it done in the next month :-/

If you solve my problem I will find you a reward (I'll admit it will most likely be in the form of kind words or stationary!)

Thanks all for reading