Perhaps provide a little bit more information, like which extension, what your LibreOffice and Linux Mint versions are, and perhaps relevant whether you are using 32-bit or 64-bit?
When I try to enable the NLPSolver extension on LibreOffice, I get the error. It also occurs when I install and enable other extensions. This is a newly installed update. Linux Mint 13 cinnamon allowed the installations.
I'm not much familiar with LibreOffice extensions, perhaps somebody else can pitch in on this. And did you install this extension from the package libreoffice-nlpsolver, or from somewhere else?