Title says it all pretty much. I'm trying to use ISO Tool to install Prometheus (Prometheus installer wasn't working; basically telling me the same thing ISO Tool is now), but when I select CFW Change, I get the message "Not on 5.00/5.03/5.50" and then it goes back to the previous menu. Any help?

I was following this guide the other day, which tells you to change the version.txt. I replaced it as it said, but at someone's suggestion changed it back to my original one (exact backup copy, no manual editing) before ever hard turning off my PSP. I also never enabled version.txt. Just mentioning that since it seems like it may be related, but I don't know what could be different now from before considering I reverted the only thing I altered without ever turning off the PSP. I've been trying to install Prometheus on and off for like 3 days now, so any help that can finally get me on my way would be very much appreciated.