There is file called "checkinfo.ini" that is causing this problem. Try and do a "All files and Folders" search in your system for this file -
checkinfo.ini
It will be in a Pentax folder. If you find it you can either rename or delete it.
When you have DCU4 open and the check-box is clicked on any of the thumbnail photos and leave it there, the “checkinfo.ini” file is created in the DCU4 folder as the application is closed. If this file is either renamed or deleted for the “fix”, a new one will be created and will cause the same problem.
To prevent the issue from reoccurring make sure there are no checks in any of the thumbnail photos before closing the program.
Hope this helps!
Cheers!