Cross-posted to the Sibelius forum:

I use Sibelius 6.2 with GPO4 on a 64 bit Dell running Windows 7. Until yesterday, it worked fine. I took a 3 week hiatus from using Sibelius and GPO - upon my return, suddenly I cannot render any instrument sounds panned to the left. They all work panned to the right, though the volume is higher than it was previously, leading to oversaturation in the playback.

If I pan an instrument to the left in the mixer, the sound disappears. Indeed, the mixer test sound is more and more soft the more leftward I adjust the pan - when I perform a hard left stereo pan in the mixer, the test yields silence. The resulting rendered wav file is oversaturated and monaural on the right stereo channel only, rendering only those instruments I have NOT set to a hard left stereo pan.

I know the problem doesn't originate with Sibelius, because I can switch the file to run the Sibelius Sound Essentials, and if I do, stereo pan works fine.

Any help that anyone can provide would be greatly appreciated -- I have a bunch of files to render for my choir, and am falling behind!