What is the name of the .dll?
 
You have different names in the title and the text.

OK, apparently the file is part of TuneUp utilities.
 
If you can boot into safe mode, try a restore point before the update.
 
 

What version of Windows?

So, you can restore the system to before the update, but it does not get rid of the error?
 
Have you tried uninstalling TuneUP?
 
Have you tried using the Windows install disc to do a Repair or Restore?

@XRayMan,
 
I saw that, but I was not sure installing another registry cleaner to fix a registry cleaner was prudent.
 
Admittedly, I have never used either one of them.

 
It's a registry error and I would try whatever I could to avoid maybe having to reinstall Windows. Unless the computer can be put back to the time before the error.

 
If he's having that much of a hard time, then I would suggest to him to reinstall Windows. It's a hassle, but it may be the only way.

might not have been so specific about the details as i should have, so this is what has happened at the moment..
 
i can´t get in to my normal windows at all.. it just gives me the error window and it doesn´t allow me to do anything. I have installed my windows again on my 2nd HDD with the CD that came with my laptop. then i found the authuitu.dll file on my primary HDD and deleted it but that didn´t solve the prob.. when i got past the "starting windows" fase i just had a black screen and a mouse and nothing happened, so i restored the file to make sure that i didn´t make the problem worse. now i´m basically back at the start again though i can access my primary windows and get the files i need if i want to. but i would just rather solve the problem than have to configure my windows again..
 
Xray man i´m gonna see if the fix you posted will work.
 
 

Good news
 
I fixed the problem..
 
I figured the problem was that the .dll file had been corrupted somehow, so i installed tuneup on my windows on the 2nd HDD so the authuitu.dll file would be made and then i copied the authuitu.dll file from my secondary windows and replaced it with the one that was on my primary windows and voila :)
 
as soon as i logged on too my primary windows i deleted the authuitu.dll file and uninstalled tuneup to prevent the problem from reappearing, so i hope that this will permanently solve the problem..
 
thanks for your advises Arctucas and XrayMan i really appreciated you guys helping me :) 

 
 Yay! Good to know it was solved!     

I wont be using it again..
 
also part of the reason i used it was because of the login screen modifications you can do with it, but i found out how to do it manually so it doesn´t really matter..