With the introduction of SMS 2.0 Service Pack 2 into your environment, you may notice that the SMSCliToknAcct& account keeps getting locked out. This is due to the absence of two .WAV files (of all things) being present in the \SYSTEM32 directory.
The files that the SMS client are looking for are the Open.wav and Close.wav files. Either copy these files from another PC in the organization to the \SYSTEM32 directory of the client computers, or create your own and copy them there
This is from Rod Trents site. I used this and it worked.