Simple Google Searches Apply Here,
Okay, if this occurs the BEST thing to do is to download Rogero's 3.55 Downgrader.
Download it put it to "USBROOT/PS3/UPDATE/PS3UPDAT.PUP"
Update via XMB. Take out discs and turn off Internet by going to "Settings" > "Network Settings" > "Internet Connection" -Disable
Then go to 3.55 KMEAW.
Going to another FW like Rogero 4.50 straight from the downgrader will result in an error halfway through the final installation.
From KMEAW go to whatever CFW you want.
If it still doesn't it appear you can always install via MultiMan by going all the way to the right and press on the "Install Pkg Files" thing, wait for it to finish, then go all the way to the left and press to install there.
IF THAT doesn't work then: Use FileZilla
Connect via FTP and transfer whatever PKGs you may have via FTP by going to
dev_hdd0/packages/<PLACETHEMHERE>
That easy. It should pop up there and then go to "File Manager" and double press it... Should install. Hope I helped!