Based only on the information contained in the error message, it appears that you are requiring the service pack download during each HI check. This would result in the file "in use" as it is in a transfer-state when trying to run it within the script.
Does your script contain an if-then statement to check for the file before you initiate the download?
Other possibilities:
The path may be incorrect in the script - test your paths by using a small .txt as your target file (for both download and opening/access)
The account that the SNAC agent runs under does not have the proper access privledges for that folder location. This would most likely occur if your organization has complex rights managment using Active Directory.
Based on the limited information, I may not fully understand the problem you are working through. Let me know if the above information if helpful or provide more info if I'm not on target.