Recently starting having this problem. 1-2 months ago it was not a problem. I am not aware of any system variables being changed.
When using the WBLOCK command, no thumbnail preview is being saved with the block for previewing in Windows Explorer. I have check the RASTERPREVIEW system variable is set to 1, but this makes no difference.
When saving files normally I do not have a problem. The block previews are very useful for my day to day work, so if anyone can help I will be very grateful. Using AutoCAD 2011.
Thanks, Gary