CIS Version 5.10 fails to update virus definitions

For several weeks now, CIS version 5.10 will not update the virus definitions either automatically or manually. It gets to 90% and then I receive message, “Failed to update the virus signature database. Please check your internet connection and try again later.” I can go online and download the full base.cav file and copy to the correct directory and CIS will show the virus date and time updated after CIS is restarted but once it tries to automatically update again, I get the same message. I have scanned my computer and found no infections. I’ve also scanned for malware and nothing was found. Any ideas to get the virus definitions to complete past 90%?