RE: "version 4.06 "
?? there is no 4.06. Where are you seeing that?
RE: "...src\Libraries\Nop.Services\Tasks\TaskThread.cs:line 71"
I don't think this error is related to your USPS config problem. This is something regarding Scheduled Tasks. Disable all the scheduled tasks. The in the systm log, note the topmost message in the log (timestamp). Now try the USPS config again, and then check the log, to see if any messages after the timestamp you noted before.