When you build a plugin on linux, you either build it 32 bit or 64 bit. If you build it 32 bit it will load in 32 bit browsers, and 64 bit will load in 64 bit browsers. You need to make sure you build it correctly for what you want.
It sounds like that's your issue -- you are trying to load a 32 bit plugin on a 64 bit process and/or vise versa. That won't work.
Unfortunately I don't know offhand how to make cmake build 32 bit on a 64 bit system.