So far all I have found is this:

Error Code 1013 System error code 1013 means "The configuration registry key could not be written." This error code may also display as "ERROR_CANTWRITE" or as the value 0x3F5.

OK - a little more digging. Found this:

This problem occurs because SUA cannot contact the mapping server during startup because the mapping server is not configured, not reachable, or has not started yet.

To work around this problem, configure the Startup type for SUA. After you do this, the Error event that is mentioned in the “Symptoms” section will no longer occur.

To configure the Startup type for SUA, follow these steps:
Click Start, click Run, type services.msc, and then click OK.
Double-click the SUA Subsystem Startup service.
Select Disabled or Manual in the Startup type box, and then click OK.

For more information: http://support.microsoft.com/kb/913001