Cannot proceed while another Task Sequence is in progress

[finners]

Have a working task sequence.  Made a copy of it, but when I try to run the copy it fail instantly.  The execmgr.log shows:

OnOptionalExecutionRequests attempted for package CAS022E3 optional program * [QueueRequest: false RunOnCompletion : true QuietMode: true SDKCallerId: (null)] execmgr 08/02/2019 09:10:08 2320 (0x0910)
Validating package CAS022E3 program * in the chain. The content request ID is {00000000-0000-0000-0000-000000000000} execmgr 08/02/2019 09:10:08 2320 (0x0910)
Creating an optional execution request for package CAS022E3 program *  execmgr 08/02/2019 09:10:08 2320 (0x0910)
Cannot proceed while another Task Sequence is in progress. execmgr 08/02/2019 09:10:08 2320 (0x0910)
OnOptionalExecutionRequests failed for program * : 0x87d01019 execmgr 08/02/2019 09:10:08 2320 (0x0910)

Troubleshooting tried so far:

-Ran powershell command which returns that there are no running task sequences.

-Can run the original task sequence no problem at all.

-Confirmed deployment settings are identical to the deployment for the original, working task sequence.

The copied TS fails so quickly it does not get as far as checking for content - no entries in cas.log etc.  Seems to be interrupted by erroneously thinking there is a TS running?  Also fails before any smsts.log.

Expect this is down to some silly error on my part that I am missing, but wanted to post incase anyone reconginizes the issue and knows what the likely cause is?