Unfortunately this issue is related to the Poser 4 renderer and the format on which it was based, when it was created on a Mac many years ago. The original Poser renderer is tightly wrapped around using the Macintosh PICT format. PICT files have a dimensional limit of 4096 pixels in either direction. Try an experiment in Photoshop by creating a PICT file larger than 4092 (a 2 pixel buffer on each side). It can't be done, even on Windows. The inherent relationship on PICT for the original Poser renderer is another reason for the new P5 Firefly renderer. Firefly has no inherent pixel limits.