It now works fine in B3 MSSQL12 - My mistake.
Thanks you both for pointing me in the right direction.

I had a typo in MSSQLDRV.int
The way i found it was to revert to a full connection string in the file.int which worked.

Then i cut and pasted that as follows
DFConnectionId ftConnectionID, SERVER=RMCDHPENVY17\SQLEXPRESS;Trusted_Connection= yes;DATABASE=PL Master Chart, 1

Then I restored the connection id in the file.int to
SERVER_NAME DFCONNID=ftConnectionID

I am also happy that I have methods to delete and create a new connection when selecting any client database from about 200 databases, similarly when creating a new database and table set using a sql script.

Once again the help was appreciated.