Solve conflict between affinity mask and I/O affinity mask?
The 'affinity mask' and 'affinity I/O mask' configuration values of
  SQL Server should not conflict. Performance may suffer if you choose
  to affinitize a processor for both SQL Server worker thread scheduling
  and for I/O processing.


What is meant by the above statement is:


  DO NOT CONFIGURE SUCH THAT A PROCESSOR IS SET IN BOTH WORKER AND
  I/O MASKS!


It's stated in the documentation and is protected from a mistyped attempt by the error message and requirement to specify WITH OVERRIDE to force the change through. That was your warning that something bad could happen.


  Msg 5834, Level 16, State 1, Line 1 The affinity mask specified
  conflicts with the IO affinity mask specified. Use the override option
  to force this configuration.


IO affinity masking is a rarely used optimisation, which offloads IO completion activity to a dedicated CPU. When set, a hidden scheduler is created that handles only IO operations for that instance. If you configure identical CPU and IO masks, the two schedulers will battle it out for CPU cycles and cause chaos.

The masks you've set are creating exactly that scenario with 1111110 specified for both. 

If your intention is the more common requirement to dedicate CPUs to particular instances on a shared server, use just the CPU affinity mask and leave the IO mask as 0 (disabled).

I've encountered a mis-configured server with matching masks only once. I was put in front of it because the logs suddenly started filling up with the message we all dread to see:


  I/O requests taking longer than 15 seconds to complete on file...


After resetting the IO mask and restarting, the server behaved perfectly and the error above was never seen again.

Useful references:


Books Online - affinity I/O mask Server Configuration Option.
CSS - How it works: IO Affinity Mask - Should I Use It?.