Ok... hmm well theres a couple different things it could be. You have to save it as the correct name, and in the right place. Make sure that if you go back to pf\menu2\ that sc_selcharacter.pac is still there, and with the same name.
Also, if you replace a file with something that isn't compatible, it might cause it to freeze. Like make sure you are putting the Etna CSP over the CSP instead of accidentally putting the Etna BP over the CSP... The CSP needs to have dimensions of 128 x 160 pixels and has to be in .PNG format.
...A problem that could be occuring, but im 99% sure isn't, is if the sc_selcharacter.pac file is too large, the game could freeze upon trying to load it. (I had this problem with the sc_selmap.pac) The reason I dont think this is your problem is because I've added dozens of CSPs with no such problem. However, feel free to look up the sc_selcharacter.pac file size limit on google or something and check to see if you're not over.
Worst comes to worst, go to the picture you replaced and replace it again with the actual picture it should be (found online somewhere)
Let me know
OK I'll try