Okular can't open files [unless executed from terminal]

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http://www.kubuntuforums.net – Hi, I recently upgraded my laptop and my workstation to 13.04 from 12.10 (64bit), and I'm having an annoying problem on my laptop (but not on my workstation!): When I try to open a PDF file using Okular from the plasma environment (from krunner, dolphin, kmail, and Firefox), I can't open any files; Okular itself starts up, but whenever I try to open a file, I get the message "Could not open /path/to/file.pdf". However, when I run Okular from the terminal and open a PDF file, it works perfectly fine. This does not happen on my workstation (although there are other problems), (HowTos)