Sure you got the correct spelling ? The lower case l looks like an i in windows
Isas.exe
isass.exe
lsass.exe
People often confuse Isass.exe and Lsass.exe. Isass.exe is a virus--so named because the lower case "L" and uppercase "I" look the same in Windows, according to SoftwarePatch.com. If you have Isass.exe on your computer, remove it immediately with anti-virus software.
http://www.ehow.com/facts_6901348_isass_exe_.html