Alex, I think the sym servers were available. Because yesterday I had the same error and concurrently I was successfuly doing (running, downloading) installation of SP1 in my testing environment.
After I created new case and this forum, I have found following RANDOM solution:
My solution:
- I skipped HF6 installation and tried to directly go through SP1 installation wizard
- and what happened, it started checking the software without error
- I stopped it immediately
- I tried to go through HF6 installation wizard again
- and BINGO! it works now, so HF6 installed
- and now the SP1 is installing.