I'm unable to reproduce this issue. I would say try again and if you can post back with any additional info on how you've setup Impulse, that would help.
1. Ok i had the full install of Impulse and SINS (v1.05) installed via Impulse aswell, enabled pre-release view of updates . The 1.09.[b].038 showed up so I tried downloading and it took some time to load and then went on to download. At 51% it stalled for 20 minutes and then gave me a download error. -> Checked the forums and read that uninstalling and reinstalling would do the trick.
2. Uninstalled SINS and tried re-installing. After the Uninstall completed Impulse under My Games Tab showed me that I could install the Entire game up to 1.09.[b].038. Clicked install and it did the predownload file build. On completion it shortly says: Downloading and then Download Error immediately after.
3. Uninstalled Impulse all together and downloaded the web installer. It downloaded and installed on my system under 2 minutes, so that server is still up and has bandwidth. After download, install and startup i was prompted, that there was an Impulse Update. Update started, Impulse restarted. then Tried above step 2: re-installing SINS... same error reported.