Okay, so i'm running CFW 3.52 M33-2, and i'm trying to update to 4.01. BUT for some reason it won't update. It suddenly get's stuck.
It says... "Unpacking... done.
Please wait... "
and then i wait... and it remains there! forever! I formatted my memory stick, for some strange reason? Any help would be greatly appreciated.

You need to have also an eboot of offical sony 4.01 firmware, i think that in the readme is clear writen, that you need also that...
You have to rename it to 401.PBP and put it into same folder - UPDATE...
If this doesn´t work try to update to 3.52m33-4 and then upgrade it...If this doesn´´t work try to redownload the file from dark alex site...If that aslo don´t work upgrade it into 3.90m33...

Yeah, i've followed the instructions correctly. I already had the official firmware. Thanks I will try what you suggested now.

okay, so i tried using a recovery flash to try update to 3.71, but my psp said I have to launch it from the XMB? Which i think i was the way i launched it. Then i tried updating (normal CFW way) with 3.71 M33, but it said "This blah blah requires 3.52M33-3 or higher... thing is my psp system information says it's running 3.52m33-4??? so now what!?

Hmm first heard for that sort of errors...
did you folowed that GUIDE

It must work...
and be sure that you have all things in recovery mode made/enabled correctly...

Hey thans for the help. Everything is sorted. Booted up in recovery. reformatted the flash and it was back to normal. Supposedly something was corrupt.