Isass.exe - system error : An invalid parameter was passed to a service or function.

To get to this point i was repairing corrupt or missing files which was : windows\system32\config\system.  I followed instructions and the commands went something like this... copy c:\windows\system32\config\system c:\windows\tmp\system.bak... and did this also with software.bak , sam.bak, security.bak, and default.bak.  i realized i messed up one of the commands when i originally wrote it down. So at restarting the computer to go throught it again and fix it this time it went to te windows loading page. when it gets here this error screen pops up that says: an invalid parameter was passed to a service or function.  I restarted my computer and booted from my windows disc to go into the repair to go throught the commands again but now it wants an Administrator password that i never set. i tried everything.  i'm at a loss. someone help...:)


Question Info

Last updated November 30, 2019 Views 23,835 Applies to:

If it is isass (note the "i") you have a virus, the correct name for the security subsystem is Lsass (note the "L") it stands for "Local Security Authority Subsystem Service".

You can mount your drive in a USB enclosure or in another computer or use a UBCD4Win boot disk to keep on trying to repair by replacing the registry hives as shown in article

Remember that the objective of the exercise described in KB 307545 is to replace the damaged registry hives in the %systemroot%\system32\config folder with the most recent backups available and then perform a proper system restore.  The most recent backup of the registry hives are located in one of the Snapshot folders in the System Volume Information folder, this is easy to do when the disk is mounted in another computer.

When the disk is mounted in another Windows installation you can dispense with Steps 1 and 3 altogether.  From the Snapshot folder copy the files:


to the System32\config folder directly, making sure to rename them as


These will in fact replace the present  DEFAULT, SECURITY, SOFTWARE, SYSTEM, and SAM files in the Config folder.

Once that is done, return the disk to the computer and if it boots proceed to Step 4 as instructed in the article.



Programmers are either not taught about Occam's razor or they forgot about it the following day.

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