There may be security apps (antivirus/antispyware/firewall) on your machine interfering with the download. SpyBot and Ad-Aware are common offendres. Try adding exclusions for Impulse.exe to any security software that you may have. If this does not help, you may need to temporarily disable this type of software to get Impulse to work. Be sure to turn it back on afterwards.
If all of this fails, try uninstalling Impulse, rebooting your PC, and then install Impulse from the full installer here: http://www.impulsedriven.com/impulse_setup_full.exe