Brian,
I suspect that what you are seeing is due to the version of a versioning conflict between CalExec and DAQmx. If you are using DAQmx 8.3.1 or newer, then you need Calibration Executive 3.2 for 6115 devices. Here's some background on why this is:
The actual calibration procedure is implemented in the driver, which CalExec calls into. We found a way to improve our calibration algorithm for 6115 devices in the driver, and this got implemented in DAQmx version 8.3.1. However, to implement this change, we needed to change the allowable value of the reference voltage applied during calibration. We used to allow any voltage between 6 V and 9.998 V. We changed this to be 5 V +/- 5 mV. The problem here is that if you are using an older version of CalExec (older than 3.2), it will apply a reference voltage in the old allowable range. If you have updated DAQmx to 8.3.1 or newer, this is no longer valid.
If this is the problem you are seeing, then there is two ways to fix it. As a first option, you could upgrade CalExec to version 3.2, which was updated to work with the new 6115's new calibration algorithm in DAQmx drivers 8.3.1 and newer. Your second option would be to back your DAQmx version down to something older than 8.3.1.
Hope this helps,
Dan