It seems likely then, that Windows is loading something during normal start-up that is blocking Secunia's access to the Internet. That Secunia won't scan is probably because one its drivers, or drivers/software that it relies on, are not loaded in Safe Mode.
A few links to check out for you:
I would definitely recommend running "sfc /scannow" just to eliminate a Windows Integriy issue.
If none of the suggestions in the two links will solve your problem, I would recommend posting in the Secunia Forums and/or contacting their Technical Support. The folks there will be much better informed than I am, and it seems not too many of the pros here on the BC Forum are familiar with Secunia. Personally, I have never used it.
Hope this is of some help. Good luck and have a great day.