Commandline Profiler says: "NV_Warning: Profiler counters are disabled for this context." ?

I’m using the Compute Commandline Profiler in CUDA Toolkit 4.2.9 in CentOS 5.6 64-bit Linux to gather statistics on my OpenCL kernel.

Does anyone know what might cause this warning to appear as the first line of my opencl_profile_2.log file:
NV_Warning: Profiler counters are disabled for this context.

OPENCL_PROFILE_LOG_VERSION 2.0

OPENCL_DEVICE 0 GeForce GTX 580

OPENCL_CONTEXT 3

TIMESTAMPFACTOR fffff6b661ce62c8

method,gputime,cputime,occupancy

And sure enough, the log for my kernels do not include any results from profiler counters, just the higher level values for memory transfers, and kernel execution times, and occupancy.
I really want to look at things like branch, and divergent_branch.

P.S. - the only google hit for that warning message was not helpful/relevant.

I figured out a plausible explanation and a workaround:

Apparently the profiler counters are only enabled for the first context created (either first overall, or first with the particular device, not sure which).

So, I changed my application to use the first (and only) OpenCL context created, and then the profile counters were available,

and their results were reported in the opencl_profile_0.log file.