PE Elan 6100 having low Cu recoveries for 6020 Interference Check

Hi all,
I would like some advice on what could be the issue when an Elan 6100 is consistently failing the Interference check B for method 6020 for Copper. I am new on this machine, and with this method, and I am trying to find out where I should check. My trainer tells me (swears up down, left and right) that it is the machine and not the solution, the question is where in the machine?
The calibration curve is good, every other analyte in the interference check solution is passing (200 ppb +/- 10%) and copper is just falling. Yesterday it barely failed at 156, today it is dropping to 145, and we need it to be at least 160 ppb. We have a new detector, the ICV/ICB is passing. It is passing the daily performance for everything, but the interference for copper is failing. And we need it so we can complete our IDL's for the 6020 method. My trainer keeps telling me it is the lens, but the lens has been cleaned, put back in, a different lens was cleaned and put back in, and it didn't change.

Any ideas on what might cause this to help a new person out on this machine?

1/ Does the same phenomenon happen on both Cu-isotopes (63 and 65)? 
2/ Are you using any mathematical correction on the copper isotopes?

1. The same phenomenon does happen on Cu 63 as well as 65.
2. As far as I can tell in the methods-equation tab we have no corrections (or equations there) for Cu.

Have you tried making and running a 200 ppb single-element Cu standard? If that passes, it will tell you that it's not the instrument.

I made a 200 ppb copper solution and it had 96% recovery with the ideal value. The ICV always passes, the standard curve looks good, and on our other elan 6100 DRC II (which isn't actually running with the DRC), the IFA/IFB solution is passing with values of 186 ppb.

If the single element solution is passing, it has to be a problem with the interference check solution, or the stock standards. Did you make the 200 ppb Cu solution from the same stock standard you use to make the interference check? I'm not familiar wht your instrument, does it have a collision/reaction cell and are you running in both hydrogen and helium mode?