When did you obtain your copy of NU15? If this is a recent install you may be able to get a free copy of NU16 which addresses several bugs of NU15. Please contact support to verify if you are eligible for a free upgrade.
As for the answer to your query, what is the rest of the string? If you send through the scan.log file, it should help in explaining why this occurs. You have to understand that a lot of software make changes to the Registry that may be uneccassry or cause slowness. By removing these minor/uneccassry changes in the registry and keeping it as clean as possible, you can have a cleaner registry data base which ensures less crashes and better performance.