It is possible to replace that file but my suspicion is that it's not lsass that is corrupt. Here's Grif with scans for the usual malware but before you do this, be sure you have your files safe.
After your files are safe then you scan for pests and try the old XP REINSTALL method (google that!)
-> http://forums.cnet.com/7726-6132_102-5098912.html?tag=posts;msg5099421
Bob
Getting this error just before the Win logon window apears:
lsass.exe Invalid parameter was passed to a service of fonction
I can access my data..using a cd I have so I can get to my data. Is there's something I can do at this level? lsass.exe is vital so I can't rename it.
If all I have is Dos what can I do?

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