Exactly how are you putting in the picture mat? Cut-n-paste? Loading from file?

The only time I ever experience something like that is when I cut-n-paste from one Bryce to another while forgetting the clipboard got cleared.

If it's the other way, while loading from a file... try different file formats. Last week I had an issue working with new coffee foam mats where one file mustive been glitched and Bryce wouldn't like it. Re-saving in the same format didn't, though. So I saved in other formats and it worked.