Many thanks.

This has been one helluva learning curve for me over the past few days digging into all of this and I'm finally getting to a stage where I can see things clearly.

What I had missed in the profier was that the settings were captured in the connection, I had presumed they were adopting the setting at database level, which was clearly wrong.

I'm now able, with the help of the dm views to get to the cached plans and can now see what is happening, where the issues might lie, and what to do about them. I can now clearly see that settings are being set by the client, and as far as I can make out, wrongly (ARITHABORT to OFF in this case as the client application is not setting this itself).

I've pretty much determined that this setting is giving me grief from a performance point of view, and also that it is masking other issues such as the way procedures have been coded and are being called (my thanks go to another poster somewhere else on giving me a heads up on this) - so the extra effort trying to understand all of this is paying off as I can now start making recommendations to them as to what needs to be done (getting them to follow it is going to be the fun part :hehe:).

I still have quite a way to go with this, but it is proving to be a fascinating experience, if not infuriating at times.