SwePeso's solution at the following link has been the best help for this.

https://www.sqlteam.com/forums/topic.asp?TOPIC_ID=145825

We created both of those keys (as they were not present), but no cigar sadly. Been Googling for most of the day!!

Thank you for your reply. Unfortunately I have been unable to locate the keys you reference (or any equivalents), throughout the whole registry?

Sue_H - the flags were definitely missing, we scripted the jobs out to check, and also stopped receiving job history information monitoring-side since the job steps were no longer logging...

Thank you all for your replies, apologies but it does appear that some of our obfuscation has resulted in the above script not accurately reproducing the same issue. In addition,...

Hi Sue, thanks very much for your advice!

TCP port 1434 was being blocked by our inter-data centre firewalls. The issue has now been fixed. Thanks to all for your help!

Hi Sue, thank you for the clarification regarding the Browser Service, that's really helpful. I modified the error message to add <namedinstance> for completeness, apologies if it was misleading. Yes...

It appears at present that TCP port 1434 is being blocked by our inter-data centre firewalls. This protocol/port has already been configured in the local firewalls. We are just waiting...

Hi Sue, yes I can confirm that this had already been enabled.
Configuration option 'remote admin connections' changed from 1 to 1. Run the RECONFIGURE statement to install.
Unfortunately...

Further information:
It turns out these errors only occur when attempting to connect to a given instance via the DAC from a different database server on the same network. We...