B_Barnes- To install, copy
both the folders (fmchanger
and fmchanger%) to either GAME or GAME150. Kernel shouldn't matter- I have tested it on either kernel in either folder on 3.71 M33-4 and it works fine with any configuration. Your error sounds like you don't have the 1.50 subset installed, which reminds me this probably won't work on slims...

If you have an original PSP, either download and install the 1.50 addon or tell us your firmware to see if we can diagnose anything else