not valid Win32 application

Hello,
I have Windows xp home edition version 2002 Service pak 2 and I have an error
When I start up or restart this is what appears on screen, clicking ok
removes it and I can work, its just a pain and I don't know how to fix it.
There aren't any viruses, but there may have been and this is what's left to
fix.

C:\Windows\System32\lvhnst\lsass.exe is not a valid Win32 application.
(This appears and says to click...I do then the following appears)

Could not load or run C:\Windows\System32\lvhnst\lsass.exe specified in the
registry. Make sure file exists on your computer or remove the reference to
it in the registry.
(click as indicated and then it disappears and I can work on pc)
Cheers,
02409395