This is down to a bug in Nero Vision Express and some other programs that customize the windows thumbnail view of picture files. To fix the Nero problem the solution is to choose the Windows "start" button, then choose "run" and paste in this:
regsvr32 /u "C:Program FilesCommon FilesAheadDSFilterNeVideo.ax"
If Nero is not the problem, another solution is to drag and drop the picture you want into Portrait Professional.
Another solution is to run this program which will stop Portrait Professional using windows thumbnails: pp6NoThumbs.exe.
The reason this only seems to happen in Portrait Professional is that when our application displays the file open dialog we automatically select the windows thumbnail view, unlike most other applications.
We do this only to help you to find the picture you want.