Sync error on dual graphics laptop

Hello everybody.

I'm kindly asking for your help for a problem of beamposition sync on a HP ProBook 650 laptop.

The laptop has Windows 7 64 bit and Matlab 2014b installed.

The laptop is equipped with a dual switchable graphic card configuration, with a power saving GPU Intel HD 4600 and an high performance GPU AMD Radeon HD 8500M/8700M.

I've installed all the latest graphics drivers, disabled Triple buffering and set the "Wait for Vertical Refresh" option to "On, unless Application specify" on both GPUs. I've also set the internal display as the main display.

I've updated Psychtoolbox to version 3.0.12 SVN Revision 5797.

When I force Matlab to use the high performance GPU VBLSyncTest stops with a sync error while if I leave Matlab to use the low performance GPU the test completes but with synchronization errors in the output.

No other applications are running in the background and the operating system has been optimized for performance disabling junk services.

I don't have any idea of how to solve this issue.

My goal is to make PTB work fine using the high performance GPU.

I attach the logs of the two situations described above obtained by running VBLSyncTest with Screen verbosity set to 10.

Many many many many many thanks in advance !!!!